------------ Pattern coercions (translation only) ---------------
| CoPat ExprCoFn -- If co::t1 -> t2, p::t2,
-- then (CoPat co p) :: t1
------------ Pattern coercions (translation only) ---------------
| CoPat ExprCoFn -- If co::t1 -> t2, p::t2,
-- then (CoPat co p) :: t1