# Properties of signomial Functions in one variable

I am interested in functions of the form: \sum_{j=1}^\infty a_j x^{p_j} where p_j can be any non-negative real number. Wikipedia has informed me that this is a subset of the signomial functions, but I have not found any references that describe their properties. For example, how general is the class of function that this includes? Are they closed under composition?

Any references would be great!

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