Some definitions of interest.
biject	Def Bij(A; B; f) == Inj(A; B; f) & Surj(A; B; f)
	Thm* A,B:Type, f:(AB). Bij(A; B; f)  Prop
inv_funs	Def InvFuns(A; B; f; g) == g o f = Id & f o g = Id
	Thm* A,B:Type, f:(AB), g:(BA). InvFuns(A; B; f; g)  Prop
compose	Def (f o g)(x) == f(g(x))
	Thm* A,B,C:Type, f:(BC), g:(AB). f o g  AC
tidentity	Def Id == Id
	Thm* A:Type. Id  AA

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