Some definitions of interest.
deq	Def EqDecider(T) == eq:TTx,y:T. x = y  (eq(x,y))
	Thm* T:Type. EqDecider(T)  Type
fpf-cap	Def f(x)?z == if x  dom(f) f(x) else z fi
eqof	Def eqof(d) == 1of(d)
	Thm* T:Type, d:EqDecider(T). eqof(d)  TT
fpf-single	Def x : v == <[x],x.v>
top	Def Top == Void given Void
	Thm* Top  Type

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