This module defines signatures that are to be included in other signatures to ensure a
consistent interface to equal functions. There is a signature (S, S1, S2,
S3) for each arity of type. Usage looks like:
type t
include Equal.S with type t := t
or
type 'a t
include Equal.S1 with type 'a t := 'a t
module type S : sig ... endmodule type S1 : sig ... endmodule type S2 : sig ... endmodule type S3 : sig ... end