Some definitions of interest.
iff	Def P  Q == (P  Q) & (P  Q)
	Thm* A,B:Prop. (A  B)  Prop
not	Def A == A  False
	Thm* A:Prop. (A)  Prop
rev_implies	Def P  Q == Q  P
	Thm* A,B:Prop. (A  B)  Prop

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