fix b70e6fca (prev commit)

alib2algo/src/regexp/RegExpDerivation.cpp

@@ -97,7 +97,7 @@ void RegExpDerivation::Visit(void* userData, const regexp::FormalRegExpConcatena
     delete leftDerivative;
     delete rightElement;
-    if(concatenation.getLeftElement().containsEmptyString())
+    if(regexp::RegExpEpsilon::languageContainsEpsilon(concatenation.getLeftElement()))
     {
         const regexp::FormalRegExpElement *alternation = out.second, *rightDerivative = nullptr;
         static_cast<const regexp::FormalRegExpElement&>(concatenation.getRightElement()).Accept(userData, *this);