private String compare(String leftHandSide, String rightHandSide) {
            if (leftHandSide.equals("integer")) {
                if (rightHandSide.equals("integer")) {
                    return "integer";
                } else if (rightHandSide.equals("real")){
                    return "real";
                } else {
                    SemanticWarningList.addWarning(SemanticWarning.makeNewWarning("Unknown type for variable '" + rightHandSide + "'. Undeclared variable."));
                }
            } else if (leftHandSide.equals("real")) {
                if (rightHandSide.equals("integer") || rightHandSide.equals("real")) {
                    return "real";
                } 
            } 
        return EMPTY;
    }