double factorial

src/main/java/org/solovyev/android/calculator/TextHighlighter.java

@@ -146,6 +146,7 @@ public class TextHighlighter implements TextProcessor<TextHighlighter.Result, St
 					if (mathType.getMathType() == MathType.text || match.length() <= 1) {
 						text1.append(text.charAt(i));
 					} else {
+						text1.append(match);
 						i += match.length() - 1;
 					}
 			}

src/main/java/org/solovyev/android/calculator/model/AndroidPostfixFunctionsRegistry.java

@@ -25,6 +25,7 @@ public class AndroidPostfixFunctionsRegistry extends AndroidMathRegistryImpl<Ope
 	static {
 		substitutes.put("%", "percent");
 		substitutes.put("!", "factorial");
+		substitutes.put("!!", "double_factorial");
 		substitutes.put("°", "degree");
 	}