rec definition length L ≝ match L with
[ LAtom ⇒ 0
-| LBind L _ â\87\92 ⫯(length L)
+| LBind L _ â\87\92 â\86\91(length L)
].
interpretation "length (local environment)" 'card L = (length L).
// qed.
(* Basic_2A1: uses: length_pair *)
-lemma length_bind: â\88\80I,L. |L.â\93\98{I}| = ⫯|L|.
+lemma length_bind: â\88\80I,L. |L.â\93\98{I}| = â\86\91|L|.
// qed.
(* Basic inversion lemmas ***************************************************)
/2 width=1 by length_inv_zero_dx/ qed-.
(* Basic_2A1: was: length_inv_pos_dx *)
-lemma length_inv_succ_dx: â\88\80n,L. |L| = ⫯n →
+lemma length_inv_succ_dx: â\88\80n,L. |L| = â\86\91n →
∃∃I,K. |K| = n & L = K. ⓘ{I}.
#n *
[ >length_atom #H destruct
qed-.
(* Basic_2A1: was: length_inv_pos_sn *)
-lemma length_inv_succ_sn: â\88\80n,L. ⫯n = |L| →
+lemma length_inv_succ_sn: â\88\80n,L. â\86\91n = |L| →
∃∃I,K. n = |K| & L = K. ⓘ{I}.
#n #L #H lapply (sym_eq ??? H) -H
#H elim (length_inv_succ_dx … H) -H /2 width=4 by ex2_2_intro/