Some definitions of interest.
ball	Def x:T. P(x) == (x:T. P(x))
	Thm* T:Type, P:(T). (x:T. P(x))
assert	Def b == if b True else False fi
	Thm* b:. b  Prop
bequal	Def x = y == (x = y  T)
	Thm* T:Type, x,y:T. (x = y)

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