Some definitions of interest.
even	Def even(n) == if n=0 then true else even(n-1) fi   (recursive)
	Thm* n:. even(n)
bnot	Def b == if b false else true fi
	Thm* b:. b
gt	Def i>j == j<i
	Thm* i,j:. (i>j)  Prop
nat	Def  == {i:| 0i }
	Thm*   Type
	Thm*   S

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