Some definitions of interest.
iff	Def  P  Q == (P  Q) & (P  Q)
	Thm*  A,B:Prop. (A  B)  Prop
int_seg	Def  {i..j} == {k:| i  k < j }
	Thm*  m,n:. {m..n}  Type
nat	Def   == {i:| 0i }
	Thm*    Type

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