Two functions which can create any computable function by composing?
If such functions existed, they would constitute a computable enumeration of all computable functions, which is impossible for the following reason. Suppose you had a computable enumeration $f_i$ of all computable functions. The function $g\colon i \mapsto f_i(i) + 1$ is then computable, but by definition $g \neq f_i$ for all $i$.