Next Obligation.
rewrite -(unitR V)/V.
have V: valid (W l1 nodes \+ W l2 nodes \+ Unit) by rewrite unitR validV.
apply: (injectR V); do?[apply: hook_complete_unit | apply: hooks_consistent_unit].
by move=>??????; rewrite dom0.
Defined.

Lemma hcomp l : hook_complete (W l nodes).
End CombineGreeters.