Some definitions of interest.
assert	Def b == if b True else False fi
	Thm* b:. b  Prop
bif	Def bif(b; bx.x(bx); by.y(by)) == if b x(*) else y(x.x) fi
	Thm* A:Type, b:, x:(bA), y:((b)A). bif(b; bx.x(bx); by.y(by))  A
not	Def A == A  False
	Thm* A:Prop. (A)  Prop

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