+{-
+foo :: (forall g a . <[ () -> a
+ PGArrow g (GArrowUnit g) a ->
+ (forall b . PGArrow g (GArrowTensor g b b) b) ->
+-}
+--foo con mer = <[ ~~mer ~~con ~~con ]>
+--foo const merge = <[ ~~merge ~~const (~~merge ~~const ~~const) ]>
+foo const merge = <[ ~~merge ~~const ~~const ]>