thing = forall x y : foo, bla x y
     : Prop
thing = 
forall (x : foo@{thing.u0}) (y : foo@{thing.u1}), bla x y
     : Prop
(* {thing.u1 thing.u0} |= bla.u0 = thing.u0
                          bla.u1 = thing.u1 *)
thing = 
forall (x : @foo@{thing.u0} True) (y : @foo@{thing.u1} True),
@bla True True x y
     : Prop
(* {thing.u1 thing.u0} |= bla.u0 = thing.u0
                          bla.u1 = thing.u1 *)