diff -r 916bebf91c41 -r 03587920dfd9 hgext/evolve.py
--- a/hgext/evolve.py	Thu Feb 27 17:20:34 2014 -0800
+++ b/hgext/evolve.py	Thu Feb 27 18:30:55 2014 -0800
@@ -682,7 +682,6 @@
     except KeyError:
         pass  # rebase not found
 
-
 #####################################################################
 ### Old Evolve extension content                                  ###
 #####################################################################
@@ -2031,3 +2030,47 @@
     entry[1].append(('O', 'old-obsolete', False,
                      _("make graft obsoletes its source")))
 
+#####################################################################
+### Obsolescence marker exchange experimenation                   ###
+#####################################################################
+
+@command('debugobsoleterelevant',
+         [],
+         'REVSET')
+def debugobsoleterelevant(ui, repo, *revsets):
+    """print allobsolescence marker relevant to a set of revision"""
+    nodes = [ctx.node() for ctx in repo.set('%lr', revsets)]
+    markers = repo.obsstore.relevantmarkers(nodes)
+    for rawmarker in sorted(markers):
+        marker = obsolete.marker(repo, rawmarker)
+        cmdutil.showmarker(ui, marker)
+
+@eh.addattr(obsolete.obsstore, 'relevantmarkers')
+def relevantmarkers(self, nodes):
+    """return a set of all obsolescence marker relevant to a set of node.
+
+    "relevant" to a set of node mean:
+
+    - marker that use this changeset as successors
+    - prune marker of direct children on this changeset.
+    - recursive application of the two rules on precursors of these markers
+
+    It  a set so you cannot rely on order"""
+    seennodes = set(nodes)
+    seenmarkers = set()
+    pendingnodes = set(nodes)
+    precursorsmarkers = self.precursors
+    prunedchildren = self.prunedchildren
+    while pendingnodes:
+        direct = set()
+        for current in pendingnodes:
+            direct.update(precursorsmarkers.get(current, ()))
+            direct.update(prunedchildren.get(current, ()))
+        direct -= seenmarkers
+        pendingnodes = set([m[0] for m in direct])
+        seenmarkers |= direct
+        pendingnodes -= seennodes
+        seennodes |= pendingnodes
+    return seenmarkers
+
+