Some definitions of interest.
assert	Def b == if b True else False fi
	Thm* b:. b  Prop
ge	Def ij == ji
	Thm* i,j:. (ij)  Prop
length	Def ||as|| == Case of as; nil  0 ; a.as'  ||as'||+1  (recursive)
	Thm* A:Type, l:A List. ||l||
	Thm* ||nil||
lt_int	Def i<j == if i<j true ; false fi
	Thm* i,j:. (i<j)

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