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+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, *   INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2015     *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+(* This module builds a VCS like interface on top of Dag, used to build
+   a Dag instance by the State Transaction Machine.
+
+   This data structure does not hold system states:
+   - Edges are meant to hold a diff.
+     The delta between two states, or equivalent data like a vernac_expr whose
+     execution corresponds to the application of the diff.
+   - Nodes are empty, unless one adds explicit info.
+     The info could be a system state, obtaind by applying all the diffs
+     from the initial state, but is not necessarily there.
+   As a consequence, "checkout" just updates the current branch.
+
+   The type [id] is the type of commits (a node in the dag)
+   The type [Vcs.t] has 3 parameters:
+    ['info] data attached to a node (like a system state)
+    ['diff] data attached to an edge (the commit content, a "patch")
+    ['kind] extra data attached to a branch (like being the master branch)
+*)
+
+module type S = sig
+
+  module Branch :
+  sig
+    type t
+    val make : string -> t
+    val equal : t -> t -> bool
+    val compare : t -> t -> int
+    val to_string : t -> string
+    val master : t
+  end
+
+  type id
+  
+  type ('kind) branch_info = {
+    kind : [> `Master] as 'kind;
+    root : id;
+    pos  : id;
+  }
+  
+  type ('kind,'diff,'info) t constraint 'kind = [> `Master ]
+  
+  val empty : id -> ('kind,'diff,'info) t
+  
+  val current_branch : ('k,'e,'i) t -> Branch.t
+  val branches : ('k,'e,'i) t -> Branch.t list
+  
+  val get_branch : ('k,'e,'i) t -> Branch.t -> 'k branch_info
+  val reset_branch : ('k,'e,'i) t -> Branch.t -> id -> ('k,'e,'i) t
+  val branch :
+    ('kind,'e,'i) t -> ?root:id -> ?pos:id ->
+        Branch.t -> 'kind -> ('kind,'e,'i) t
+  val delete_branch : ('k,'e,'i) t -> Branch.t -> ('k,'e,'i) t
+  val merge :
+    ('k,'diff,'i) t -> id -> ours:'diff -> theirs:'diff -> ?into:Branch.t ->
+            Branch.t -> ('k,'diff,'i) t
+  val commit : ('k,'diff,'i) t -> id -> 'diff -> ('k,'diff,'i) t
+  val rewrite_merge :
+    ('k,'diff,'i) t -> id -> ours:'diff -> theirs:'diff -> at:id ->
+            Branch.t -> ('k,'diff,'i) t
+  val checkout : ('k,'e,'i) t -> Branch.t -> ('k,'e,'i) t
+  
+  val set_info : ('k,'e,'info) t -> id -> 'info -> ('k,'e,'info) t
+  val get_info : ('k,'e,'info) t -> id -> 'info option
+
+  module NodeSet : Set.S with type elt = id
+  
+  (* Removes all unreachable nodes and returns them *)
+  val gc : ('k,'e,'info) t -> ('k,'e,'info) t * NodeSet.t
+
+  val reachable : ('k,'e,'info) t -> id -> NodeSet.t
+
+  (* read only dag *)
+  module Dag : Dag.S with type node = id
+  val dag : ('kind,'diff,'info) t -> ('diff,'info,id * id) Dag.t
+ 
+  val create_cluster : ('k,'e,'i) t -> id list -> (id * id) -> ('k,'e,'i) t
+  val cluster_of : ('k,'e,'i) t -> id -> (id * id) Dag.Cluster.t option
+  val delete_cluster : ('k,'e,'i) t -> (id * id) Dag.Cluster.t -> ('k,'e,'i) t 
+
+end
+
+module Make(OT : Map.OrderedType) : S with type id = OT.t