optCoercion :: TvSubst -> Coercion -> NormalCo\r
-- ^ optCoercion applies a substitution to a coercion, \r
-- *and* optimises it to reduce its size\r
optCoercion :: TvSubst -> Coercion -> NormalCo\r
-- ^ optCoercion applies a substitution to a coercion, \r
-- *and* optimises it to reduce its size\r