Std.FrontierFrontier maps each node into a possibly empty set of nodes. This is used for representing dominance and post-dominance frontiers.
type 'a t = 'a frontierval enum : 'a t -> 'a -> 'a Regular.Std.seqenum f x enumerates frontier of x
val mem : 'a t -> 'a -> 'a -> boolmem f x y is true if y is in a frontier of x
val to_sequence : 'a t -> 'a Regular.Std.seqto_sequence frontier enumerates all elements of a frontier
val pp : 'a Regular.Std.printer -> 'a t Regular.Std.printerpp pp_elt instantiates a pretty-printer for a given element. See Tree.pp for more information.