code: public Expression convertToMutableBooleanExpression(ImmutableExpression booleanExpression) {
          OperationPredicate pred = booleanExpression.getFunctionSymbol();
          return termFactory.getExpression(pred, convertToMutableTerms(booleanExpression.getTerms()));
      }
docs: This method takes a immutable boolean term and convert it into an old mutable boolean function.