milestone uupdate in basic_2

[helm.git] / matita / matita / contribs / lambdadelta / basic_2 / rt_computation / cpms_cpms.ma

diff --git a/matita/matita/contribs/lambdadelta/basic_2/rt_computation/cpms_cpms.ma b/matita/matita/contribs/lambdadelta/basic_2/rt_computation/cpms_cpms.ma
index a9f2d248c6715acef109ff5bb9fb9e73f9edba9b..fcd97f3b905b5192dc3c7cc908bfebe0ef7bab2a 100644 (file)
--- a/matita/matita/contribs/lambdadelta/basic_2/rt_computation/cpms_cpms.ma
+++ b/matita/matita/contribs/lambdadelta/basic_2/rt_computation/cpms_cpms.ma
@@ -168,3 +168,11 @@ theorem cpms_cast (n) (h) (G) (L):
   /3 width=3 by cpms_trans, cpms_cast_sn/
 ]
 qed.
+
+theorem cpms_trans_swap (h) (G) (L) (T1):
+        ∀n1,T. ⦃G,L⦄ ⊢ T1 ➡*[n1,h] T → ∀n2,T2. ⦃G,L⦄ ⊢ T ➡*[n2,h] T2 →
+        ∃∃T0. ⦃G,L⦄ ⊢ T1 ➡*[n2,h] T0 & ⦃G,L⦄ ⊢ T0 ➡*[n1,h] T2.
+#h #G #L #T1 #n1 #T #HT1 #n2 #T2 #HT2
+lapply (cpms_trans … HT1 … HT2) -T <commutative_plus #HT12
+/2 width=1 by cpms_inv_plus/
+qed-.