initConditionFunctions();
generalFunctions = new HashSet<Function>(conditionFunctions);
// add AddFunction
generalFunctions.addAll((new AddFunctionCluster()).getSupportedFunctions());
// add SubtractFunction
generalFunctions.addAll((new SubtractFunctionCluster()).getSupportedFunctions());
// add MultiplyFunction
generalFunctions.addAll((new MultiplyFunctionCluster()).getSupportedFunctions());
// add DivideFunction