data Symmetrise : Rel a -> Rel a
Fwd : r x y -> Symmetrise r x y
Bwd : r x y -> Symmetrise r y x
sym : Symmetrise r ~> flip (Symmetrise r)
gmap : (f : (a -> b)) -> p ~> (q `on` f) -> Symmetrise p ~> (Symmetrise q `on` f)
map : p ~> q -> Symmetrise p ~> Symmetrise q
join : Symmetrise (Symmetrise p) ~> Symmetrise p