Some definitions of interest.
divides	Def b | a == c:. a = bc
	Thm* a,b:. (a | b)  Prop
nat	Def  == {i:| 0i }
	Thm*   Type
le	Def AB == B<A
	Thm* i,j:. (ij)  Prop
nat_plus	Def  == {i:| 0<i }
	Thm*   Type

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