diff --git a/pom.xml b/pom.xml
index 226bf92d..40d7c787 100644
--- a/pom.xml
+++ b/pom.xml
@@ -15,8 +15,24 @@
 		<additionalLibs>${basedir}/src/misc/lib</additionalLibs>
 	</properties>
 
+	<repositories>
+		<repository>
+			<id>congrace.de</id>
+			<name>releases</name>
+			<url>http://nexus.congrace.de/nexus/content/repositories/releases/</url>
+			<layout>default</layout>
+		</repository>
+	</repositories>
+
 	<dependencies>
 
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<version>4.8.2</version>
+			<scope>test</scope>
+		</dependency>
+
 		<dependency>
 			<groupId>org.solovyev</groupId>
 			<artifactId>common</artifactId>
@@ -37,6 +53,12 @@
 			<systemPath>${additionalLibs}/jscl.jar</systemPath>
 		</dependency>
 
+		<dependency>
+			<groupId>de.congrace</groupId>
+			<artifactId>exp4j</artifactId>
+			<version>0.2.8</version>
+		</dependency>
+
 		<dependency>
 			<groupId>com.intellij</groupId>
 			<artifactId>annotations</artifactId>
diff --git a/res/layout-land/main.xml b/res/layout-land/main.xml
index d72988fb..281323cd 100644
--- a/res/layout-land/main.xml
+++ b/res/layout-land/main.xml
@@ -38,7 +38,7 @@
 														   style="@style/control_button_style"
 														   a:onClick="eraseButtonClickHandler"/>
 
-			<TextView
+			<org.solovyev.android.calculator.CalculatorDisplay
 					a:id="@+id/resultEditText"
 					style="@style/display_style"
 					a:gravity="right|top"
@@ -75,8 +75,8 @@
 														   calc:textDown="acos" style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
-			<org.solovyev.android.view.DirectionDragButton a:id="@+id/threeDigitButton" a:text="3" calc:textUp="tg"
-														   calc:textDown="atg" style="@style/digit_button_style"
+			<org.solovyev.android.view.DirectionDragButton a:id="@+id/threeDigitButton" a:text="3" calc:textUp="tan"
+														   calc:textDown="atan" style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/multiplicationButton" a:text="×"
@@ -106,20 +106,22 @@
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/fourDigitButton"
 														   a:text="4"
-														   calc:textUp=""
-														   calc:textDown=""
+														   calc:textUp="sinh"
+														   calc:textDown="asinh"
 														   style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/fiveDigitButton"
 														   a:text="5"
-														   calc:textUp="ln"
+														   calc:textUp="cosh"
+														   calc:textDown="acosh"
 														   style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/sixDigitButton" a:text="6"
-														   calc:textUp=""
-														   calc:textDown="" style="@style/digit_button_style"
+														   calc:textUp="tanh"
+														   calc:textDown="atanh"
+														   style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/plusButton" a:text="+"
@@ -147,12 +149,16 @@
 
 		<LinearLayout a:layout_weight="1" a:layout_width="match_parent" a:layout_height="0dp">
 
-			<org.solovyev.android.view.DirectionDragButton a:id="@+id/sevenDigitButton" a:text="7" calc:textUp=""
-														   calc:textDown="" style="@style/digit_button_style"
+			<org.solovyev.android.view.DirectionDragButton a:id="@+id/sevenDigitButton" a:text="7"
+														   calc:textUp="i"
+														   calc:textDown=""
+														   style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
-			<org.solovyev.android.view.DirectionDragButton a:id="@+id/eightDigitButton" a:text="8" calc:textUp=""
-														   calc:textDown="" style="@style/digit_button_style"
+			<org.solovyev.android.view.DirectionDragButton a:id="@+id/eightDigitButton" a:text="8"
+														   calc:textUp="ln"
+														   calc:textDown=""
+														   style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/nineDigitButton" a:text="9"
diff --git a/res/layout-port/main.xml b/res/layout-port/main.xml
index 935cdd0b..35ed91cd 100644
--- a/res/layout-port/main.xml
+++ b/res/layout-port/main.xml
@@ -33,7 +33,7 @@
 														   style="@style/control_button_style"
 														   a:onClick="numericButtonClickHandler"/>
 
-			<TextView
+			<org.solovyev.android.calculator.CalculatorDisplay
 					a:id="@+id/resultEditText"
 					style="@style/display_style"
 					a:gravity="right|top"
@@ -56,8 +56,8 @@
 														   calc:textDown="acos" style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
-			<org.solovyev.android.view.DirectionDragButton a:id="@+id/threeDigitButton" a:text="3" calc:textUp="tg"
-														   calc:textDown="atg" style="@style/digit_button_style"
+			<org.solovyev.android.view.DirectionDragButton a:id="@+id/threeDigitButton" a:text="3" calc:textUp="tan"
+														   calc:textDown="atan" style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/multiplicationButton" a:text="×"
@@ -76,20 +76,22 @@
 			
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/fourDigitButton"
 														   a:text="4"
-														   calc:textUp=""
-														   calc:textDown=""
+														   calc:textUp="sinh"
+														   calc:textDown="asinh"
 														   style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/fiveDigitButton"
 														   a:text="5"
-														   calc:textUp="ln"
+														   calc:textUp="cosh"
+														   calc:textDown="acosh"
 														   style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/sixDigitButton" a:text="6"
-														   calc:textUp=""
-														   calc:textDown="" style="@style/digit_button_style"
+														   calc:textUp="tanh"
+														   calc:textDown="atanh"
+														   style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/divisionButton" a:text="/"
@@ -106,12 +108,16 @@
 
 		<LinearLayout a:layout_weight="1" a:layout_width="match_parent" a:layout_height="0dp">
 
-			<org.solovyev.android.view.DirectionDragButton a:id="@+id/sevenDigitButton" a:text="7" calc:textUp=""
-														   calc:textDown="" style="@style/digit_button_style"
+			<org.solovyev.android.view.DirectionDragButton a:id="@+id/sevenDigitButton" a:text="7"
+														   calc:textUp="i"
+														   calc:textDown=""
+														   style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
-			<org.solovyev.android.view.DirectionDragButton a:id="@+id/eightDigitButton" a:text="8" calc:textUp=""
-														   calc:textDown="" style="@style/digit_button_style"
+			<org.solovyev.android.view.DirectionDragButton a:id="@+id/eightDigitButton" a:text="8"
+														   calc:textUp="ln"
+														   calc:textDown=""
+														   style="@style/digit_button_style"
 														   a:onClick="digitButtonClickHandler"/>
 
 			<org.solovyev.android.view.DirectionDragButton a:id="@+id/nineDigitButton" a:text="9"
diff --git a/res/values/strings.xml b/res/values/strings.xml
index e6dd71f6..1fb71d86 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -2,7 +2,8 @@
 <resources>
     <string name="c_app_name">Calculator</string>
     <string name="c_app_settings">Calculator</string>
-    <string name="syntax_error">Syntax error</string>
+    <string name="c_syntax_error">Syntax error</string>
+    <string name="c_result_copied">Result copied to clipboard!</string>
 	<string name="c_settings">Settings</string>
 	<string name="c_help">Help</string>
 	<string name="c_prefs_main_category">Main settings</string>
diff --git a/res/values/styles.xml b/res/values/styles.xml
index 7bf09d88..eb061e64 100644
--- a/res/values/styles.xml
+++ b/res/values/styles.xml
@@ -27,7 +27,7 @@
     </style>
 
     <style name="display_style">
-        <item name="android:textSize">30dp</item>
+        <item name="android:textSize">25dp</item>
         <item name="android:background">#000000</item>
         <item name="android:textColor">#ffffff</item>
         <item name="android:gravity">left|top</item>
diff --git a/src/main/java/org/solovyev/android/calculator/CalculatorDisplay.java b/src/main/java/org/solovyev/android/calculator/CalculatorDisplay.java
new file mode 100644
index 00000000..3dd32d57
--- /dev/null
+++ b/src/main/java/org/solovyev/android/calculator/CalculatorDisplay.java
@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2009-2011. Created by serso aka se.solovyev.
+ * For more information, please, contact se.solovyev@gmail.com
+ */
+
+package org.solovyev.android.calculator;
+
+import android.content.Context;
+import android.util.AttributeSet;
+import android.widget.TextView;
+
+/**
+ * User: serso
+ * Date: 9/17/11
+ * Time: 10:58 PM
+ */
+public class CalculatorDisplay extends TextView {
+
+	private boolean valid = true;
+
+	public CalculatorDisplay(Context context) {
+		super(context);
+	}
+
+	public CalculatorDisplay(Context context, AttributeSet attrs) {
+		super(context, attrs);
+	}
+
+	public CalculatorDisplay(Context context, AttributeSet attrs, int defStyle) {
+		super(context, attrs, defStyle);
+	}
+
+	public boolean isValid() {
+		return valid;
+	}
+
+	public void setValid(boolean valid) {
+		this.valid = valid;
+	}
+
+	@Override
+	public void setText(CharSequence text, BufferType type) {
+		super.setText(text, type);
+
+		setValid(true);
+	}
+}
diff --git a/src/main/java/org/solovyev/android/calculator/CalculatorDisplayHistoryState.java b/src/main/java/org/solovyev/android/calculator/CalculatorDisplayHistoryState.java
new file mode 100644
index 00000000..e1c05a1c
--- /dev/null
+++ b/src/main/java/org/solovyev/android/calculator/CalculatorDisplayHistoryState.java
@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2009-2011. Created by serso aka se.solovyev.
+ * For more information, please, contact se.solovyev@gmail.com
+ */
+
+package org.solovyev.android.calculator;
+
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * User: serso
+ * Date: 9/17/11
+ * Time: 11:05 PM
+ */
+public class CalculatorDisplayHistoryState extends EditorHistoryState {
+
+	private boolean valid = true;
+
+	public CalculatorDisplayHistoryState() {
+	}
+
+	public CalculatorDisplayHistoryState(boolean valid) {
+		this.valid = valid;
+	}
+
+	public CalculatorDisplayHistoryState(int cursorPosition, @Nullable String text, boolean valid) {
+		super(cursorPosition, text);
+		this.valid = valid;
+	}
+
+	public boolean isValid() {
+		return valid;
+	}
+
+	public void setValid(boolean valid) {
+		this.valid = valid;
+	}
+}
diff --git a/src/main/java/org/solovyev/android/calculator/CalculatorHistoryState.java b/src/main/java/org/solovyev/android/calculator/CalculatorHistoryState.java
index 7478ce70..3e7136bf 100644
--- a/src/main/java/org/solovyev/android/calculator/CalculatorHistoryState.java
+++ b/src/main/java/org/solovyev/android/calculator/CalculatorHistoryState.java
@@ -18,9 +18,9 @@ public class CalculatorHistoryState {
 	private EditorHistoryState editorState;
 
 	@NotNull
-	private EditorHistoryState displayState;
+	private CalculatorDisplayHistoryState displayState;
 
-	public CalculatorHistoryState(@NotNull EditorHistoryState editorState, @NotNull EditorHistoryState displayState) {
+	public CalculatorHistoryState(@NotNull EditorHistoryState editorState, @NotNull CalculatorDisplayHistoryState displayState) {
 		this.editorState = editorState;
 		this.displayState = displayState;
 	}
@@ -35,11 +35,11 @@ public class CalculatorHistoryState {
 	}
 
 	@NotNull
-	public EditorHistoryState getDisplayState() {
+	public CalculatorDisplayHistoryState getDisplayState() {
 		return displayState;
 	}
 
-	public void setDisplayState(@NotNull EditorHistoryState displayState) {
+	public void setDisplayState(@NotNull CalculatorDisplayHistoryState displayState) {
 		this.displayState = displayState;
 	}
 }
diff --git a/src/main/java/org/solovyev/android/calculator/CalculatorModel.java b/src/main/java/org/solovyev/android/calculator/CalculatorModel.java
index 7a65f1be..27948fe4 100644
--- a/src/main/java/org/solovyev/android/calculator/CalculatorModel.java
+++ b/src/main/java/org/solovyev/android/calculator/CalculatorModel.java
@@ -5,13 +5,13 @@
 
 package org.solovyev.android.calculator;
 
-import android.util.Log;
 import bsh.EvalError;
 import bsh.Interpreter;
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
 import org.solovyev.common.exceptions.SersoException;
 import org.solovyev.common.utils.MathUtils;
+import org.solovyev.common.utils.StringUtils;
+import org.solovyev.util.math.Complex;
 
 /**
  * User: serso
@@ -32,28 +32,76 @@ public class CalculatorModel {
 		interpreter.eval(Preprocessor.wrap(JsclOperation.importCommands, "/jscl/editorengine/commands"));
 	}
 
-	public String evaluate(@NotNull JsclOperation operation, @NotNull String expression ) throws EvalError, ParseException {
+	public String evaluate(@NotNull JsclOperation operation, @NotNull String expression) throws EvalError, ParseException {
 
 		final String preprocessedExpression = Preprocessor.process(expression);
 
-		Log.d(CalculatorModel.class.getName(), "Preprocessed expression: " + preprocessedExpression);
+		//Log.d(CalculatorModel.class.getName(), "Preprocessed expression: " + preprocessedExpression);
 
 		Object evaluationObject = interpreter.eval(Preprocessor.wrap(operation, preprocessedExpression));
 		String result = String.valueOf(evaluationObject).trim();
 
 		try {
-			final Double dResult = Double.valueOf(result);
-			result = String.valueOf(MathUtils.round(dResult, NUMBER_OF_FRACTION_DIGITS));
+			result = round(result);
 		} catch (NumberFormatException e) {
-			throw new ParseException(e);
+			if (result.contains("sqrt(-1)")) {
+				try {
+					result = createResultForComplexNumber(result.replace("sqrt(-1)", "i"));
+				} catch (NumberFormatException e1) {
+					// throw original one
+					throw new ParseException(e);
+				}
+
+			} else {
+				throw new ParseException(e);
+			}
 		}
 
 		return result;
 	}
 
+	public String createResultForComplexNumber(@NotNull final String s) {
+		final Complex complex = new Complex();
+
+		String result = "";
+		// may be it's just complex number
+		int plusIndex = s.lastIndexOf("+");
+		if (plusIndex >= 0) {
+			complex.setReal(round(s.substring(0, plusIndex)));
+			result += complex.getReal();
+			result += "+";
+		} else {
+			plusIndex = s.lastIndexOf("-");
+			if (plusIndex >= 0) {
+				complex.setReal(round(s.substring(0, plusIndex)));
+				result += complex.getReal();
+				result += "-";
+			}
+		}
+
+
+		int multiplyIndex = s.indexOf("*");
+		if (multiplyIndex >= 0) {
+			complex.setImag(round(s.substring(plusIndex >= 0 ? plusIndex+1 : 0, multiplyIndex)));
+			result += complex.getImag();
+
+		}
+
+		result += "i";
+
+		return result;
+	}
+
+	private String round(@NotNull String result) {
+		final Double dResult = Double.valueOf(result);
+		result = String.valueOf(MathUtils.round(dResult, NUMBER_OF_FRACTION_DIGITS));
+		return result;
+	}
+
 	public static class ParseException extends SersoException {
 		public ParseException(Throwable cause) {
 			super(cause);
 		}
 	}
+
 }
diff --git a/src/main/java/org/solovyev/android/calculator/CalculatorView.java b/src/main/java/org/solovyev/android/calculator/CalculatorView.java
index 17b7725e..86f87d70 100644
--- a/src/main/java/org/solovyev/android/calculator/CalculatorView.java
+++ b/src/main/java/org/solovyev/android/calculator/CalculatorView.java
@@ -21,7 +21,6 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.solovyev.android.view.CursorControl;
 import org.solovyev.android.view.HistoryControl;
-import org.solovyev.common.math.calculators.Calculator;
 import org.solovyev.common.utils.MutableObject;
 import org.solovyev.common.utils.StringUtils;
 import org.solovyev.common.utils.history.HistoryAction;
@@ -37,13 +36,13 @@ import org.solovyev.util.math.MathEntityType;
 public class CalculatorView implements CursorControl, HistoryControl<CalculatorHistoryState> {
 
 	// millis to wait before evaluation after user edit action
-	public static final int EVAL_DELAY_MILLIS = 1000;
+	public static final int EVAL_DELAY_MILLIS = 500;
 
 	@NotNull
 	private final CalculatorEditText editor;
 
 	@NotNull
-	private final TextView display;
+	private final CalculatorDisplay display;
 
 	@NotNull
 	private final Activity activity;
@@ -52,7 +51,7 @@ public class CalculatorView implements CursorControl, HistoryControl<CalculatorH
 	private final CalculatorModel calculatorModel;
 
 	@NotNull
-	private HistoryHelper<CalculatorHistoryState> history;
+	private final HistoryHelper<CalculatorHistoryState> history;
 
 	public CalculatorView(@NotNull final Activity activity, @NotNull CalculatorModel calculator) {
 		this.activity = activity;
@@ -64,15 +63,17 @@ public class CalculatorView implements CursorControl, HistoryControl<CalculatorH
 		this.editor.setInputType(InputType.TYPE_NULL);
 		imm.hideSoftInputFromWindow(this.editor.getWindowToken(), 0);
 
-		this.display = (TextView) activity.findViewById(R.id.resultEditText);
+		this.display = (CalculatorDisplay) activity.findViewById(R.id.resultEditText);
 		this.display.setOnClickListener(new View.OnClickListener() {
 			@Override
 			public void onClick(View v) {
-				final CharSequence text = ((TextView) v).getText();
-				if (!StringUtils.isEmpty(text)) {
-					final ClipboardManager clipboard = (ClipboardManager) activity.getSystemService(Activity.CLIPBOARD_SERVICE);
-					clipboard.setText(text);
-					Toast.makeText(activity, "Result copied to clipboard!", Toast.LENGTH_SHORT).show();
+				if (((CalculatorDisplay) v).isValid()) {
+					final CharSequence text = ((TextView) v).getText();
+					if (!StringUtils.isEmpty(text)) {
+						final ClipboardManager clipboard = (ClipboardManager) activity.getSystemService(Activity.CLIPBOARD_SERVICE);
+						clipboard.setText(text);
+						Toast.makeText(activity, "Result copied to clipboard!", Toast.LENGTH_SHORT).show();
+					}
 				}
 			}
 		});
@@ -120,17 +121,21 @@ public class CalculatorView implements CursorControl, HistoryControl<CalculatorH
 			currentRunner.setObject(new Runnable() {
 				@Override
 				public void run() {
+					// allow only one runner at one time
 					synchronized (currentRunner) {
-						// do only if nothing was post delayed before current instance was posted
-						if (currentRunner.getObject() == this) {
-							// actually nothing shall be logged while text operations are done
-							evaluate(editorStateAfter, true);
+						//lock all operations with history
+						synchronized (history) {
+							// do only if nothing was post delayed before current instance was posted
+							if (currentRunner.getObject() == this) {
+								// actually nothing shall be logged while text operations are done
+								evaluate(editorStateAfter);
 
-							if (history.isUndoAvailable()) {
-								history.undo(getCurrentHistoryState());
+								if (history.isUndoAvailable()) {
+									history.undo(getCurrentHistoryState());
+								}
+
+								saveHistoryState();
 							}
-
-							saveHistoryState();
 						}
 					}
 				}
@@ -142,29 +147,26 @@ public class CalculatorView implements CursorControl, HistoryControl<CalculatorH
 		}
 	}
 
-	private void evaluate(@Nullable final String expression, final boolean showError) {
+	private void evaluate(@Nullable final String expression) {
 		if (!StringUtils.isEmpty(expression)) {
 
-			final TextView localDisplay = display;
-			final Activity localActivity = activity;
+			final CalculatorDisplay localDisplay = display;
 
 			try {
 				Log.d(CalculatorView.class.getName(), "Trying to evaluate: " + expression);
 				localDisplay.setText(calculatorModel.evaluate(JsclOperation.numeric, expression));
 			} catch (EvalError e) {
-				handleEvaluationException(expression, showError, localDisplay, localActivity, e);
+				handleEvaluationException(expression, localDisplay, e);
 			} catch (CalculatorModel.ParseException e) {
-				handleEvaluationException(expression, showError, localDisplay, localActivity, e);
+				handleEvaluationException(expression, localDisplay, e);
 			}
 		}
 	}
 
-	private void handleEvaluationException(@NotNull String expression, boolean showError, @NotNull TextView localDisplay, @NotNull Activity localActivity, @NotNull Exception e) {
+	private void handleEvaluationException(@NotNull String expression, @NotNull CalculatorDisplay localDisplay, @NotNull Exception e) {
 		Log.d(CalculatorView.class.getName(), "Evaluation failed for : " + expression + ". Error message: " + e.getMessage());
-		localDisplay.setText("");
-		if (showError) {
-			Toast.makeText(localActivity, R.string.syntax_error, Toast.LENGTH_SHORT).show();
-		}
+		localDisplay.setText(R.string.c_syntax_error);
+		localDisplay.setValid(false);
 	}
 
 	public void clear() {
@@ -176,7 +178,7 @@ public class CalculatorView implements CursorControl, HistoryControl<CalculatorH
 	}
 
 	public void evaluate() {
-		evaluate(editor.getText().toString(), true);
+		evaluate(editor.getText().toString());
 	}
 
 	public void processDigitButtonAction(@Nullable final String text) {
@@ -223,18 +225,27 @@ public class CalculatorView implements CursorControl, HistoryControl<CalculatorH
 
 	@Override
 	public void doHistoryAction(@NotNull HistoryAction historyAction) {
-		if (history.isActionAvailable(historyAction)) {
-			final CalculatorHistoryState newState = history.doAction(historyAction, getCurrentHistoryState());
-			if (newState != null) {
-				setCurrentHistoryState(newState);
+		synchronized (history) {
+			if (history.isActionAvailable(historyAction)) {
+				final CalculatorHistoryState newState = history.doAction(historyAction, getCurrentHistoryState());
+				if (newState != null) {
+					setCurrentHistoryState(newState);
+				}
 			}
 		}
 	}
 
 	@Override
 	public void setCurrentHistoryState(@NotNull CalculatorHistoryState editorHistoryState) {
-		setValuesFromHistory(this.editor, editorHistoryState.getEditorState());
-		setValuesFromHistory(this.display, editorHistoryState.getDisplayState());
+		synchronized (history) {
+			setValuesFromHistory(this.editor, editorHistoryState.getEditorState());
+			setValuesFromHistory(this.display, editorHistoryState.getDisplayState());
+		}
+	}
+
+	private void setValuesFromHistory(@NotNull CalculatorDisplay display, CalculatorDisplayHistoryState editorHistoryState) {
+		setValuesFromHistory(display, (EditorHistoryState)editorHistoryState);
+		display.setValid(editorHistoryState.isValid());
 	}
 
 	private void setValuesFromHistory(@NotNull TextView editText, EditorHistoryState editorHistoryState) {
@@ -247,7 +258,9 @@ public class CalculatorView implements CursorControl, HistoryControl<CalculatorH
 	@Override
 	@NotNull
 	public CalculatorHistoryState getCurrentHistoryState() {
-		return new CalculatorHistoryState(getEditorHistoryState(this.editor), getEditorHistoryState(this.display));
+		synchronized (history) {
+			return new CalculatorHistoryState(getEditorHistoryState(this.editor), getCalculatorDisplayHistoryState(this.display));
+		}
 	}
 
 	private EditorHistoryState getEditorHistoryState(@NotNull TextView textView) {
@@ -258,4 +271,14 @@ public class CalculatorView implements CursorControl, HistoryControl<CalculatorH
 
 		return result;
 	}
+
+	private CalculatorDisplayHistoryState getCalculatorDisplayHistoryState(@NotNull CalculatorDisplay display) {
+		final CalculatorDisplayHistoryState result = new CalculatorDisplayHistoryState();
+
+		result.setText(String.valueOf(display.getText()));
+		result.setCursorPosition(display.getSelectionStart());
+		result.setValid(display.isValid());
+
+		return result;
+	}
 }
diff --git a/src/main/java/org/solovyev/android/calculator/Preprocessor.java b/src/main/java/org/solovyev/android/calculator/Preprocessor.java
index 895c178b..235efeb8 100644
--- a/src/main/java/org/solovyev/android/calculator/Preprocessor.java
+++ b/src/main/java/org/solovyev/android/calculator/Preprocessor.java
@@ -6,6 +6,11 @@
 package org.solovyev.android.calculator;
 
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import org.solovyev.common.utils.CollectionsUtils;
+import org.solovyev.common.utils.EqualsFinder;
+import org.solovyev.common.utils.Finder;
+import org.solovyev.util.math.Functions;
 import org.solovyev.util.math.MathEntityType;
 
 public class Preprocessor {
@@ -14,49 +19,75 @@ public class Preprocessor {
 	public static String process(@NotNull String s) {
 		final StringBuilder sb = new StringBuilder();
 
+		final StartWithFinder startsWithFinder = new StartWithFinder(s);
 		for (int i = 0; i < s.length(); i++) {
 			char ch = s.charAt(i);
 
 			checkMultiplicationSignBeforeFunction(sb, s, i);
 
-			if (ch == '[' || ch == '{') {
+			if (MathEntityType.openGroupSymbols.contains(ch)) {
 				sb.append('(');
-			} else if (ch == ']' || ch == '}') {
+			} else if (MathEntityType.closeGroupSymbols.contains(ch)) {
 				sb.append(')');
 			} else if (ch == 'π') {
 				sb.append("pi");
 			} else if (ch == '×' || ch == '∙') {
 				sb.append("*");
-			} else if (s.startsWith("ln", i)) {
-				sb.append("log");
-				i += 1;
-			} else if (s.startsWith("tg", i)) {
-				sb.append("tan");
-				i += 1;
-			} else if (s.startsWith("atg", i)) {
-				sb.append("atan");
-				i += 2;
-			} else if (s.startsWith("acos", i)) {
-				sb.append("acos");
-				i += 3;
-			} else if (s.startsWith("asin", i)) {
-				sb.append("asin");
-				i += 3;
-			} else if (s.startsWith("e(", i)) {
-				sb.append("exp(");
-				i += 1;
-			} else if (ch == 'e') {
-				sb.append("exp(1)");
-			} else if (ch == '√') {
-				sb.append("sqrt");
 			} else {
-				sb.append(ch);
+				startsWithFinder.setI(i);
+				final String function = CollectionsUtils.get(MathEntityType.functions, startsWithFinder);
+				if (function != null) {
+					sb.append(toJsclFunction(function));
+					i += function.length() - 1;
+				} else if (ch == 'e') {
+					sb.append("exp(1)");
+				} else if (ch == 'i') {
+					sb.append("sqrt(-1)");
+				} else {
+					sb.append(ch);
+				}
 			}
 		}
 
 		return sb.toString();
 	}
 
+	@NotNull
+	private static String toJsclFunction(@NotNull String function) {
+		final String result;
+
+		if (function.equals(Functions.LN)) {
+			result = Functions.LOG;
+		} else if (function.equals(Functions.SQRT_SIGN)) {
+			result = Functions.SQRT;
+		} else {
+			result = function;
+		}
+
+		return result;
+	}
+
+	private static class StartWithFinder implements Finder<String> {
+
+		private int i;
+
+		@NotNull
+		private final String targetString;
+
+		private StartWithFinder(@NotNull String targetString) {
+			this.targetString = targetString;
+		}
+
+		@Override
+		public boolean isFound(@Nullable String s) {
+			return targetString.startsWith(s, i);
+		}
+
+		public void setI(int i) {
+			this.i = i;
+		}
+	}
+
 	private static void checkMultiplicationSignBeforeFunction(@NotNull StringBuilder sb, @NotNull String s, int i) {
 		if (i > 0) {
 			// get character before function
diff --git a/src/main/java/org/solovyev/util/math/Complex.java b/src/main/java/org/solovyev/util/math/Complex.java
new file mode 100644
index 00000000..0834b8ef
--- /dev/null
+++ b/src/main/java/org/solovyev/util/math/Complex.java
@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2009-2011. Created by serso aka se.solovyev.
+ * For more information, please, contact se.solovyev@gmail.com
+ */
+
+package org.solovyev.util.math;
+
+import org.jetbrains.annotations.Nullable;
+
+/**
+* User: serso
+* Date: 9/17/11
+* Time: 11:35 PM
+*/
+public class Complex {
+
+	@Nullable
+	private String real, imag;
+
+	@Nullable
+	public String getReal() {
+		return real;
+	}
+
+	public void setReal(@Nullable String real) {
+		this.real = real;
+	}
+
+	@Nullable
+	public String getImag() {
+		return imag;
+	}
+
+	public void setImag(@Nullable String imag) {
+		this.imag = imag;
+	}
+}
diff --git a/src/main/java/org/solovyev/util/math/Functions.java b/src/main/java/org/solovyev/util/math/Functions.java
new file mode 100644
index 00000000..962a5ced
--- /dev/null
+++ b/src/main/java/org/solovyev/util/math/Functions.java
@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2009-2011. Created by serso aka se.solovyev.
+ * For more information, please, contact se.solovyev@gmail.com
+ */
+
+package org.solovyev.util.math;
+
+import org.jetbrains.annotations.NonNls;
+
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * User: serso
+ * Date: 9/17/11
+ * Time: 10:01 PM
+ */
+public interface Functions {
+
+	String SIN = "sin";
+	String SINH = "sinh";
+	String ASIN = "asin";
+	String ASINH = "asinh";
+	String COS = "cos";
+	String COSH = "cosh";
+	String ACOS = "acos";
+	String ACOSH = "acosh";
+	String TAN = "tan";
+	String TANH = "tanh";
+	String ATAN = "atan";
+	String ATANH = "atanh";
+	String LOG = "log";
+	String LN = "ln";
+	String MOD = "mod";
+	String EXP = "exp";
+	String SQRT_SIGN = "√";
+	String SQRT = "sqrt";
+
+	public static final List<String> all = Arrays.asList(SIN, SINH, ASIN, ASINH, COS, COSH, ACOS, ACOSH, TAN, TANH, ATAN, ATANH, LOG, LN, MOD, SQRT, SQRT_SIGN, EXP);
+}
diff --git a/src/main/java/org/solovyev/util/math/MathEntity.java b/src/main/java/org/solovyev/util/math/MathEntity.java
deleted file mode 100644
index 4cce1a86..00000000
--- a/src/main/java/org/solovyev/util/math/MathEntity.java
+++ /dev/null
@@ -1,42 +0,0 @@
-/*
- * Copyright (c) 2009-2011. Created by serso aka se.solovyev.
- * For more information, please, contact se.solovyev@gmail.com
- */
-
-package org.solovyev.util.math;
-
-import org.jetbrains.annotations.NotNull;
-
-public enum MathEntity {
-
-	minus("-"),
-	equals("="),
-	factorial("!"),
-	plus("+"),
-	multiply("*"),
-	divide("/"),
-	power("^"),
-	sin("sin"),
-	asin("asin"),
-	cos("cos"),
-	acos("acos"),
-	tg("tg"),
-	atg("atg"),
-	exp("exp"),
-	log("log"),
-	ln("ln"),
-	mod("mod"),
-	sqrt("sqrt");
-		
-	@NotNull
-	private final String text;
-	
-	private MathEntity (@NotNull String text) {
-		this.text = text;
-	}
-
-	@NotNull
-	public String getText() {
-		return text;
-	}
-}
diff --git a/src/main/java/org/solovyev/util/math/MathEntityType.java b/src/main/java/org/solovyev/util/math/MathEntityType.java
index c42ae38e..5d2c39e9 100644
--- a/src/main/java/org/solovyev/util/math/MathEntityType.java
+++ b/src/main/java/org/solovyev/util/math/MathEntityType.java
@@ -24,7 +24,7 @@ public enum MathEntityType {
 	group_symbols,
 	group_symbol;
 	
-	public static final List<Character> constants = Arrays.asList('e', 'π');
+	public static final List<Character> constants = Arrays.asList('e', 'π', 'i');
 
 	public static final List<Character> dots = Arrays.asList('.', ',');
 
@@ -32,8 +32,8 @@ public enum MathEntityType {
 
 	public static final List<Character> binaryOperations = Arrays.asList('-', '+', '*', '×', '∙', '/', '^' );
 
-	public static final List<String> functions = Arrays.asList("sin", "asin", "cos", "acos", "tg", "atg", "log", "ln", "mod", "√");
-	
+	public static final List<String> functions = Functions.all;
+
 	public static final List<String> groupSymbols = Arrays.asList("[]", "()", "{}");
 
 	public static final List<Character> openGroupSymbols = Arrays.asList('[', '(', '{');
diff --git a/src/test/java/org/solovyev/android/calculator/CalculatorModelTest.java b/src/test/java/org/solovyev/android/calculator/CalculatorModelTest.java
new file mode 100644
index 00000000..444dd996
--- /dev/null
+++ b/src/test/java/org/solovyev/android/calculator/CalculatorModelTest.java
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2009-2011. Created by serso aka se.solovyev.
+ * For more information, please, contact se.solovyev@gmail.com
+ */
+
+package org.solovyev.android.calculator;
+
+import de.congrace.exp4j.Calculable;
+import de.congrace.exp4j.ExpressionBuilder;
+import de.congrace.exp4j.UnknownFunctionException;
+import de.congrace.exp4j.UnparsableExpressionException;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * User: serso
+ * Date: 9/17/11
+ * Time: 9:47 PM
+ */
+public class CalculatorModelTest {
+	@Test
+	public void testEvaluate() throws Exception {
+		final CalculatorModel cm = new CalculatorModel();
+
+		Assert.assertEquals("4.0", cm.evaluate(JsclOperation.numeric, "2+2"));
+		Assert.assertEquals("-0.7568", cm.evaluate(JsclOperation.numeric, "sin(4)"));
+		Assert.assertEquals("0.5236", cm.evaluate(JsclOperation.numeric, "asin(0.5)"));
+		Assert.assertEquals("-0.39626", cm.evaluate(JsclOperation.numeric, "sin(4)asin(0.5)"));
+		Assert.assertEquals("-0.5604", cm.evaluate(JsclOperation.numeric, "sin(4)asin(0.5)sqrt(2)"));
+		Assert.assertEquals("-0.5604", cm.evaluate(JsclOperation.numeric, "sin(4)asin(0.5)√(2)"));
+		Assert.assertEquals("7.38906", cm.evaluate(JsclOperation.numeric, "e^2"));
+		Assert.assertEquals("7.38906", cm.evaluate(JsclOperation.numeric, "exp(1)^2"));
+		Assert.assertEquals("7.38906", cm.evaluate(JsclOperation.numeric, "exp(2)"));
+		Assert.assertEquals("2.0+i", cm.evaluate(JsclOperation.numeric, "2*1+sqrt(-1)"));
+		Assert.assertEquals("0.92054+3.14159i", cm.evaluate(JsclOperation.numeric, "ln(5cosh(38π√(2cos(2))))"));
+		Assert.assertEquals("7.38906i", cm.evaluate(JsclOperation.numeric, "iexp(2)"));
+		Assert.assertEquals("2.0+7.38906i", cm.evaluate(JsclOperation.numeric, "2+iexp(2)"));
+		Assert.assertEquals("2.0+7.38906i", cm.evaluate(JsclOperation.numeric, "2+√(-1)exp(2)"));
+		Assert.assertEquals("2.0-2.5i", cm.evaluate(JsclOperation.numeric, "2-2.5i"));
+		Assert.assertEquals("-2.0-2.5i", cm.evaluate(JsclOperation.numeric, "-2-2.5i"));
+		Assert.assertEquals("-2.0+2.5i", cm.evaluate(JsclOperation.numeric, "-2+2.5i"));
+		Assert.assertEquals("-2.0+2.1i", cm.evaluate(JsclOperation.numeric, "-2+2.1i"));
+		Assert.assertEquals("-3.41007+3.41007i", cm.evaluate(JsclOperation.numeric, "(5tan(2i)+2i)/(1-i)"));
+		Assert.assertEquals("-0.1-0.2i", cm.evaluate(JsclOperation.numeric, "(1-i)/(2+6i)"));
+
+	}
+
+	@Test
+	public void testComplexNumbers() throws Exception {
+		final CalculatorModel cm = new CalculatorModel();
+
+		Assert.assertEquals("1.22133+23123.0i", cm.createResultForComplexNumber("1.22133232+23123*i"));
+		Assert.assertEquals("1.22133+1.2i", cm.createResultForComplexNumber("1.22133232+1.2*i"));
+		Assert.assertEquals("1.22i", cm.createResultForComplexNumber("1.22*i"));
+		Assert.assertEquals("i", cm.createResultForComplexNumber("i"));
+
+	}
+}