Iddsmodule Bdd : sig ... endReduced Ordered Binary Decision Diagrams (BDDs).
module Boolean : sig ... endmodule Dd : sig ... endDecision Diagrams (DDs).
module Idd : sig ... endIdentity Suppressed Decision Diagrams (IDDs).
module Var : sig ... endBoolean variable on which a DD can branch. Morally just an integer, but kept abstract for safety.