Section INVARIANT3.

Lemma sigma_rooted_fun12 :
forall s1 s2 : Site,
s2 <> owner ->
s1 <> owner ->
only_once Site eq_site_dec s2 LS ->
sigma_but Site owner eq_site_dec LS (fun s : Site => rooted_fun s s1 s2 dec) =
1%Z.