Some definitions of interest.
ball	Def x:T. P(x) == (x:T. P(x))
	Thm* T:Type, P:(T). (x:T. P(x))
bimplies	Def pq == p  q
	Thm* p,q:. pq
bor	Def p  q == if p true else q fi
	Thm* p,q:. (p  q)
tlambda	Def (x:T. b(x))(x) == b(x)

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