Some definitions of interest.
decidable	Def Dec(P) == P  P
	Thm* A:Prop. Dec(A)  Prop
sq_stable	Def SqStable(P) == P  P
	Thm* A:Prop. SqStable(A)  Prop
stable	Def Stable{P} == P  P
	Thm* A:Prop. Stable{A}  Prop

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