ary) pattern to switch between the following
-- two patterns. The resulting structure comes from the binary
-- pattern, not the source patterns. See also @sew@.
stitch :: Pattern Bool -> Pattern a -> Pattern a -> Pattern a
stitch pb a b = overlay (struct pb a)  (struct (inv pb) b)

-- | A binary pattern 
stitch :: Pattern Bool -> Pattern a -> Pattern a -> Pattern a
stitch pb a b = overlay (struct pb a)  (struct (inv pb) b)
stitch pb a b = overlay (struct pb a)  (struct (inv pb) b)