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

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