public override IEnumerable <IFormulaToken> Tokenize()
{
return(Enumerable.Repeat(CreateToken(), 1)
.Concat(Enumerable.Repeat(FormulaTokenFactory.CreateParenthesisToken(true), 1))
.Concat(FirstChild == null ? FormulaTokenizer.EmptyChild : FirstChild.Tokenize())
.Concat(Enumerable.Repeat(FormulaTokenFactory.CreateParameterSeparatorToken(), 1))
.Concat(SecondChild == null ? FormulaTokenizer.EmptyChild : SecondChild.Tokenize())
.Concat(Enumerable.Repeat(FormulaTokenFactory.CreateParenthesisToken(false), 1)));
}