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diff --git a/matita/matita/contribs/lambdadelta/basic_2/i_static/tc_lfxs_tc_lfxs.ma b/matita/matita/contribs/lambdadelta/basic_2/i_static/tc_lfxs_tc_lfxs.ma
index 62173d926..09039c5e3 100644
--- a/matita/matita/contribs/lambdadelta/basic_2/i_static/tc_lfxs_tc_lfxs.ma
+++ b/matita/matita/contribs/lambdadelta/basic_2/i_static/tc_lfxs_tc_lfxs.ma
@@ -12,10 +12,20 @@
 (*                                                                        *)
 (**************************************************************************)
 
+include "basic_2/static/lfxs_lfxs.ma".
 include "basic_2/i_static/tc_lfxs.ma".
 
 (* ITERATED EXTENSION ON REFERRED ENTRIES OF A CONTEXT-SENSITIVE REALTION ***)
 
+(* Advanced properties ******************************************************)
+
+lemma tc_lfxs_sym: ∀R. lfxs_fsle_compatible R →
+                   (∀L1,L2,T1,T2. R L1 T1 T2 → R L2 T2 T1) →
+                   ∀T. symmetric … (tc_lfxs R T).
+#R #H1R #H2R #T #L1 #L2 #H elim H -L2
+/4 width=3 by lfxs_sym, tc_lfxs_step_sn, inj/
+qed-.
+
 (* Main properties **********************************************************)
 
 theorem tc_lfxs_trans: ∀R,T. Transitive … (tc_lfxs R T).