Bottom.Top
Lattices in which both top and bottom are managed separately
val join :
('a -> 'a -> 'a) ->
'a or_top_bottom ->
'a or_top_bottom ->
'a or_top_bottom
val narrow :
('a -> 'a -> 'a or_bottom) ->
'a or_top_bottom ->
'a or_top_bottom ->
'a or_top_bottom