public function makeNode($leftOperand, $rightOperand)
    {
        if ($rightOperand === null) return $this->createUnaryMinusNode($leftOperand);

        $leftOperand = $this->sanitize($leftOperand);
        $rightOperand = $this->sanitize($rightOperand);

        $node = $this->numericTerms($leftOperand, $rightOperand);
        if ($node) return $node;

        if ($leftOperand->compareTo($rightOperand)) {
            return new IntegerNode(0);
        }

        return new ExpressionNode($leftOperand, '-', $rightOperand);
    }