Some definitions of interest.
fun_exp	Def f^n == primrec(n;x.x;i,g. f o g)
	Thm* T:Type, n:, f:(TT). f^n  TT
compose	Def (f o g)(x) == f(g(x))
	Thm* A,B,C:Type, f:(BC), g:(AB). f o g  AC
nat	Def  == {i:| 0i }
	Thm*   Type

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