X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;ds=sidebyside;f=matita%2Fmatita%2Fcontribs%2Flambda%2Fpointer_order.ma;h=ddcc3fd9ec2c2ee1d19370b5b7631222c620ccf8;hb=23e75ebc00553e178e090ca1373ac075ee650a60;hp=9d79e9dc61b11a60cd60341e7fb484e52a83db6b;hpb=178820be7648a60af17837727e51fd1f3f2791db;p=helm.git

diff --git a/matita/matita/contribs/lambda/pointer_order.ma b/matita/matita/contribs/lambda/pointer_order.ma
index 9d79e9dc6..ddcc3fd9e 100644
--- a/matita/matita/contribs/lambda/pointer_order.ma
+++ b/matita/matita/contribs/lambda/pointer_order.ma
@@ -33,6 +33,13 @@ notation "hvbox(a break ≺ b)"
    non associative with precedence 45
    for @{ 'prec $a $b }.
 
+lemma pprec_fwd_in_head: ∀p,q. p ≺ q → in_head q → in_head p.
+#p #q #H elim H -p -q // /2 width=1/
+[ #p #q * #H destruct
+| #c #p #q #_ #IHpq * #H destruct /3 width=1/
+]
+qed-.
+
 (* Note: this is p < q *)
 definition plt: relation ptr ≝ TC … pprec.
 
@@ -45,11 +52,15 @@ definition ple: relation ptr ≝ star … pprec.
 interpretation "'less or equal to' on redex pointers"
    'leq p q = (ple p q).
 
-lemma pprec_ple: ∀p,q. p ≺ q → p ≤ q.
+lemma ple_step_rc: ∀p,q. p ≺ q → p ≤ q.
 /2 width=1/
 qed.
 
-lemma ple_dx: dx::◊ ≤ ◊.
+lemma ple_step_sn: ∀p1,p,p2. p1 ≺ p → p ≤ p2 → p1 ≤ p2.
+/2 width=3/
+qed-.
+
+lemma ple_skip: dx::◊ ≤ ◊.
 /2 width=1/
 qed.
 
@@ -60,3 +71,21 @@ qed.
 lemma ple_comp: ∀p1,p2. p1 ≤ p2 → ∀c. (c::p1) ≤ (c::p2).
 #p1 #p2 #H elim H -p2 // /3 width=3/
 qed.
+
+lemma ple_skip_ple: ∀p. p ≤ ◊ → dx::p ≤ ◊.
+#p #H @(star_ind_l ??????? H) -p //
+#p #q #Hpq #_ #H @(ple_step_sn … H) -H /2 width=1/
+qed.
+
+lemma in_head_ple_nil: ∀p. in_head p → p ≤ ◊.
+#p #H @(in_head_ind … H) -p // /2 width=1/
+qed.
+
+theorem in_head_ple: ∀p. in_head p → ∀q. in_head q → p ≤ q.
+#p #H @(in_head_ind … H) -p //
+#p #Hp #IHp #q #H @(in_head_ind … H) -q /3 width=1/
+qed.
+
+lemma ple_nil_inv_in_head: ∀p. p ≤ ◊ → in_head p.
+#p #H @(star_ind_l ??????? H) -p // /2 width=3 by pprec_fwd_in_head/
+qed-.