Some definitions of interest.
absval	Def |i| == if 0i i else -i fi
	Thm* x:. |x|
nat	Def  == {i:| 0i }
	Thm*   Type
wellfounded	Def WellFnd{i}(A;x,y.R(x;y)) Def == P:(AProp). (j:A. (k:A. R(k;j)  P(k))  P(j))  {n:A. P(n)}
	Thm* A:Type{i}, r:(AAProp{i}). WellFnd{i}(A;x,y.r(x,y))  Prop{i'}

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