Some definitions of interest.
iff	Def  P  Q == (P  Q) & (P  Q)
	Thm*  A,B:Prop. (A  B)  Prop
lelt	Def  i  j < k == ij & j<k
le	Def  AB == B<A
	Thm*  i,j:. (ij)  Prop
one_one_corr_2	Def  A ~ B == f:(AB), g:(BA). InvFuns(A;B;f;g)
	Thm*  A,B:Type. (A ~ B)  Prop

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