- degree-based equivalene for terms

[helm.git] / matita / matita / contribs / lambdadelta / basic_2 / etc_2A1 / tshf / chnf.etc

diff --git a/matita/matita/contribs/lambdadelta/basic_2/etc_2A1/tshf/chnf.etc b/matita/matita/contribs/lambdadelta/basic_2/etc_2A1/tshf/chnf.etc
new file mode 100644 (file)
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+(**************************************************************************)
+(*       ___                                                              *)
+(*      ||M||                                                             *)
+(*      ||A||       A project by Andrea Asperti                           *)
+(*      ||T||                                                             *)
+(*      ||I||       Developers:                                           *)
+(*      ||T||         The HELM team.                                      *)
+(*      ||A||         http://helm.cs.unibo.it                             *)
+(*      \   /                                                             *)
+(*       \ /        This file is distributed under the terms of the       *)
+(*        v         GNU General Public License Version 2                  *)
+(*                                                                        *)
+(**************************************************************************)
+
+notation "hvbox( L ⊢ break 𝐇𝐍 ⦃ term 46 T ⦄ )"
+   non associative with precedence 45
+   for @{ 'HdNormal $L $T }.
+
+include "basic_2/reduction/cpr_tshf.ma".
+
+(* CONTEXT-SENSITIVE WEAK HEAD NORMAL TERMS *********************************)
+
+definition chnf: lenv → predicate term ≝ λL. NF … (cpr L) tshf.
+
+interpretation
+   "context-sensitive head normality (term)"
+   'HdNormal L T = (chnf L T).
+
+(* Basic inversion lemmas ***************************************************)
+
+lemma chnf_inv_tshf: ∀L,T. L ⊢ 𝐇𝐍⦃T⦄ → T ≈ T.
+normalize /2 width=1/
+qed-.
+
+(* Basic properties *********************************************************)
+
+lemma tshf_thnf: ∀T. T ≈ T → ⋆ ⊢ 𝐇𝐍⦃T⦄.
+#T #HT #T2 #H elim (cpr_fwd_tshf1 … H) -H //
+#H elim H //
+qed.