Some definitions of interest.
IdLnk	Def IdLnk == IdId
	Thm* IdLnk  Type
Id	Def Id == Atom
	Thm* Id  Type
assert	Def b == if b True else False fi
	Thm* b:. b  Prop
fun_exp	Def f^n == primrec(n;x.x;i,g. f o g)
	Thm* T:Type, n:, f:(TT). f^n  TT
ldst	Def destination(l) == 1of(2of(l))
	Thm* l:IdLnk. destination(l)  Id
lsrc	Def source(l) == 1of(l)
	Thm* l:IdLnk. source(l)  Id
nat_plus	Def  == {i:| 0<i }
	Thm*   Type

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