Some definitions of interest.
assert	Def b == if b True else False fi
	Thm* b:. b  Prop
hzero_rep	Def zero_rep == @x:. (y:. x = suc_rep(y)  )
	Thm* zero_rep  hind
hsuc_rep	Def suc_rep == x:. (@f:. (one_one(;;f) & onto(;;f)))(x)
	Thm* suc_rep  (hind  hind)
nat	Def  == {i:| 0i }
	Thm*   Type
	Thm*   S
ncompose	Def ncompose(f;n;x) == if n=0 then x else f(ncompose(f;n-1;x)) fi   (recursive)
	Thm* 'a:Type, n:, x:'a, f:('a'a). ncompose(f;n;x)  'a

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