X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=matita%2Fmatita%2Fcontribs%2Flambdadelta%2Fbasic_2%2Fsubstitution%2Flsuby.ma;h=623f8c6aa734680505c86b5059ce0797218a980c;hb=c60524dec7ace912c416a90d6b926bee8553250b;hp=578612a71b8c5b2688858b264027d1ec55d9f9a6;hpb=f10cfe417b6b8ec1c7ac85c6ecf5fb1b3fdf37db;p=helm.git diff --git a/matita/matita/contribs/lambdadelta/basic_2/substitution/lsuby.ma b/matita/matita/contribs/lambdadelta/basic_2/substitution/lsuby.ma index 578612a71..623f8c6aa 100644 --- a/matita/matita/contribs/lambdadelta/basic_2/substitution/lsuby.ma +++ b/matita/matita/contribs/lambdadelta/basic_2/substitution/lsuby.ma @@ -19,29 +19,29 @@ include "basic_2/substitution/drop.ma". (* LOCAL ENVIRONMENT REFINEMENT FOR EXTENDED SUBSTITUTION *******************) inductive lsuby: relation4 ynat ynat lenv lenv ≝ -| lsuby_atom: ∀L,d,e. lsuby d e L (⋆) +| lsuby_atom: ∀L,l,m. lsuby l m L (⋆) | lsuby_zero: ∀I1,I2,L1,L2,V1,V2. lsuby 0 0 L1 L2 → lsuby 0 0 (L1.ⓑ{I1}V1) (L2.ⓑ{I2}V2) -| lsuby_pair: ∀I1,I2,L1,L2,V,e. lsuby 0 e L1 L2 → - lsuby 0 (⫯e) (L1.ⓑ{I1}V) (L2.ⓑ{I2}V) -| lsuby_succ: ∀I1,I2,L1,L2,V1,V2,d,e. - lsuby d e L1 L2 → lsuby (⫯d) e (L1.ⓑ{I1}V1) (L2.ⓑ{I2}V2) +| lsuby_pair: ∀I1,I2,L1,L2,V,m. lsuby 0 m L1 L2 → + lsuby 0 (⫯m) (L1.ⓑ{I1}V) (L2.ⓑ{I2}V) +| lsuby_succ: ∀I1,I2,L1,L2,V1,V2,l,m. + lsuby l m L1 L2 → lsuby (⫯l) m (L1.ⓑ{I1}V1) (L2.ⓑ{I2}V2) . interpretation "local environment refinement (extended substitution)" - 'LRSubEq L1 d e L2 = (lsuby d e L1 L2). + 'LRSubEq L1 l m L2 = (lsuby l m L1 L2). (* Basic properties *********************************************************) -lemma lsuby_pair_lt: ∀I1,I2,L1,L2,V,e. L1 ⊆[0, ⫰e] L2 → 0 < e → - L1.ⓑ{I1}V ⊆[0, e] L2.ⓑ{I2}V. -#I1 #I2 #L1 #L2 #V #e #HL12 #He <(ylt_inv_O1 … He) /2 width=1 by lsuby_pair/ +lemma lsuby_pair_lt: ∀I1,I2,L1,L2,V,m. L1 ⊆[0, ⫰m] L2 → 0 < m → + L1.ⓑ{I1}V ⊆[0, m] L2.ⓑ{I2}V. +#I1 #I2 #L1 #L2 #V #m #HL12 #Hm <(ylt_inv_O1 … Hm) /2 width=1 by lsuby_pair/ qed. -lemma lsuby_succ_lt: ∀I1,I2,L1,L2,V1,V2,d,e. L1 ⊆[⫰d, e] L2 → 0 < d → - L1.ⓑ{I1}V1 ⊆[d, e] L2. ⓑ{I2}V2. -#I1 #I2 #L1 #L2 #V1 #V2 #d #e #HL12 #Hd <(ylt_inv_O1 … Hd) /2 width=1 by lsuby_succ/ +lemma lsuby_succ_lt: ∀I1,I2,L1,L2,V1,V2,l,m. L1 ⊆[⫰l, m] L2 → 0 < l → + L1.ⓑ{I1}V1 ⊆[l, m] L2. ⓑ{I2}V2. +#I1 #I2 #L1 #L2 #V1 #V2 #l #m #HL12 #Hl <(ylt_inv_O1 … Hl) /2 width=1 by lsuby_succ/ qed. lemma lsuby_pair_O_Y: ∀L1,L2. L1 ⊆[0, ∞] L2 → @@ -49,57 +49,57 @@ lemma lsuby_pair_O_Y: ∀L1,L2. L1 ⊆[0, ∞] L2 → #L1 #L2 #HL12 #I1 #I2 #V lapply (lsuby_pair I1 I2 … V … HL12) -HL12 // qed. -lemma lsuby_refl: ∀L,d,e. L ⊆[d, e] L. +lemma lsuby_refl: ∀L,l,m. L ⊆[l, m] L. #L elim L -L // -#L #I #V #IHL #d elim (ynat_cases … d) [| * #x ] -#Hd destruct /2 width=1 by lsuby_succ/ -#e elim (ynat_cases … e) [| * #x ] -#He destruct /2 width=1 by lsuby_zero, lsuby_pair/ +#L #I #V #IHL #l elim (ynat_cases … l) [| * #x ] +#Hl destruct /2 width=1 by lsuby_succ/ +#m elim (ynat_cases … m) [| * #x ] +#Hm destruct /2 width=1 by lsuby_zero, lsuby_pair/ qed. -lemma lsuby_O2: ∀L2,L1,d. |L2| ≤ |L1| → L1 ⊆[d, yinj 0] L2. +lemma lsuby_O2: ∀L2,L1,l. |L2| ≤ |L1| → L1 ⊆[l, yinj 0] L2. #L2 elim L2 -L2 // #L2 #I2 #V2 #IHL2 * normalize -[ #d #H elim (le_plus_xSy_O_false … H) -| #L1 #I1 #V1 #d #H lapply (le_plus_to_le_r … H) -H #HL12 - elim (ynat_cases d) /3 width=1 by lsuby_zero/ +[ #l #H elim (le_plus_xSy_O_false … H) +| #L1 #I1 #V1 #l #H lapply (le_plus_to_le_r … H) -H #HL12 + elim (ynat_cases l) /3 width=1 by lsuby_zero/ * /3 width=1 by lsuby_succ/ ] qed. -lemma lsuby_sym: ∀d,e,L1,L2. L1 ⊆[d, e] L2 → |L1| = |L2| → L2 ⊆[d, e] L1. -#d #e #L1 #L2 #H elim H -d -e -L1 -L2 -[ #L1 #d #e #H >(length_inv_zero_dx … H) -L1 // +lemma lsuby_sym: ∀l,m,L1,L2. L1 ⊆[l, m] L2 → |L1| = |L2| → L2 ⊆[l, m] L1. +#l #m #L1 #L2 #H elim H -l -m -L1 -L2 +[ #L1 #l #m #H >(length_inv_zero_dx … H) -L1 // | /2 width=1 by lsuby_O2/ -| #I1 #I2 #L1 #L2 #V #e #_ #IHL12 #H lapply (injective_plus_l … H) +| #I1 #I2 #L1 #L2 #V #m #_ #IHL12 #H lapply (injective_plus_l … H) /3 width=1 by lsuby_pair/ -| #I1 #I2 #L1 #L2 #V1 #V2 #d #e #_ #IHL12 #H lapply (injective_plus_l … H) +| #I1 #I2 #L1 #L2 #V1 #V2 #l #m #_ #IHL12 #H lapply (injective_plus_l … H) /3 width=1 by lsuby_succ/ ] qed-. (* Basic inversion lemmas ***************************************************) -fact lsuby_inv_atom1_aux: ∀L1,L2,d,e. L1 ⊆[d, e] L2 → L1 = ⋆ → L2 = ⋆. -#L1 #L2 #d #e * -L1 -L2 -d -e // +fact lsuby_inv_atom1_aux: ∀L1,L2,l,m. L1 ⊆[l, m] L2 → L1 = ⋆ → L2 = ⋆. +#L1 #L2 #l #m * -L1 -L2 -l -m // [ #I1 #I2 #L1 #L2 #V1 #V2 #_ #H destruct -| #I1 #I2 #L1 #L2 #V #e #_ #H destruct -| #I1 #I2 #L1 #L2 #V1 #V2 #d #e #_ #H destruct +| #I1 #I2 #L1 #L2 #V #m #_ #H destruct +| #I1 #I2 #L1 #L2 #V1 #V2 #l #m #_ #H destruct ] qed-. -lemma lsuby_inv_atom1: ∀L2,d,e. ⋆ ⊆[d, e] L2 → L2 = ⋆. +lemma lsuby_inv_atom1: ∀L2,l,m. ⋆ ⊆[l, m] L2 → L2 = ⋆. /2 width=5 by lsuby_inv_atom1_aux/ qed-. -fact lsuby_inv_zero1_aux: ∀L1,L2,d,e. L1 ⊆[d, e] L2 → - ∀J1,K1,W1. L1 = K1.ⓑ{J1}W1 → d = 0 → e = 0 → +fact lsuby_inv_zero1_aux: ∀L1,L2,l,m. L1 ⊆[l, m] L2 → + ∀J1,K1,W1. L1 = K1.ⓑ{J1}W1 → l = 0 → m = 0 → L2 = ⋆ ∨ ∃∃J2,K2,W2. K1 ⊆[0, 0] K2 & L2 = K2.ⓑ{J2}W2. -#L1 #L2 #d #e * -L1 -L2 -d -e /2 width=1 by or_introl/ +#L1 #L2 #l #m * -L1 -L2 -l -m /2 width=1 by or_introl/ [ #I1 #I2 #L1 #L2 #V1 #V2 #HL12 #J1 #K1 #W1 #H #_ #_ destruct /3 width=5 by ex2_3_intro, or_intror/ -| #I1 #I2 #L1 #L2 #V #e #_ #J1 #K1 #W1 #_ #_ #H +| #I1 #I2 #L1 #L2 #V #m #_ #J1 #K1 #W1 #_ #_ #H elim (ysucc_inv_O_dx … H) -| #I1 #I2 #L1 #L2 #V1 #V2 #d #e #_ #J1 #K1 #W1 #_ #H +| #I1 #I2 #L1 #L2 #V1 #V2 #l #m #_ #J1 #K1 #W1 #_ #H elim (ysucc_inv_O_dx … H) ] qed-. @@ -109,54 +109,54 @@ lemma lsuby_inv_zero1: ∀I1,K1,L2,V1. K1.ⓑ{I1}V1 ⊆[0, 0] L2 → ∃∃I2,K2,V2. K1 ⊆[0, 0] K2 & L2 = K2.ⓑ{I2}V2. /2 width=9 by lsuby_inv_zero1_aux/ qed-. -fact lsuby_inv_pair1_aux: ∀L1,L2,d,e. L1 ⊆[d, e] L2 → - ∀J1,K1,W. L1 = K1.ⓑ{J1}W → d = 0 → 0 < e → +fact lsuby_inv_pair1_aux: ∀L1,L2,l,m. L1 ⊆[l, m] L2 → + ∀J1,K1,W. L1 = K1.ⓑ{J1}W → l = 0 → 0 < m → L2 = ⋆ ∨ - ∃∃J2,K2. K1 ⊆[0, ⫰e] K2 & L2 = K2.ⓑ{J2}W. -#L1 #L2 #d #e * -L1 -L2 -d -e /2 width=1 by or_introl/ + ∃∃J2,K2. K1 ⊆[0, ⫰m] K2 & L2 = K2.ⓑ{J2}W. +#L1 #L2 #l #m * -L1 -L2 -l -m /2 width=1 by or_introl/ [ #I1 #I2 #L1 #L2 #V1 #V2 #_ #J1 #K1 #W #_ #_ #H elim (ylt_yle_false … H) // -| #I1 #I2 #L1 #L2 #V #e #HL12 #J1 #K1 #W #H #_ #_ destruct +| #I1 #I2 #L1 #L2 #V #m #HL12 #J1 #K1 #W #H #_ #_ destruct /3 width=4 by ex2_2_intro, or_intror/ -| #I1 #I2 #L1 #L2 #V1 #V2 #d #e #_ #J1 #K1 #W #_ #H +| #I1 #I2 #L1 #L2 #V1 #V2 #l #m #_ #J1 #K1 #W #_ #H elim (ysucc_inv_O_dx … H) ] qed-. -lemma lsuby_inv_pair1: ∀I1,K1,L2,V,e. K1.ⓑ{I1}V ⊆[0, e] L2 → 0 < e → +lemma lsuby_inv_pair1: ∀I1,K1,L2,V,m. K1.ⓑ{I1}V ⊆[0, m] L2 → 0 < m → L2 = ⋆ ∨ - ∃∃I2,K2. K1 ⊆[0, ⫰e] K2 & L2 = K2.ⓑ{I2}V. + ∃∃I2,K2. K1 ⊆[0, ⫰m] K2 & L2 = K2.ⓑ{I2}V. /2 width=6 by lsuby_inv_pair1_aux/ qed-. -fact lsuby_inv_succ1_aux: ∀L1,L2,d,e. L1 ⊆[d, e] L2 → - ∀J1,K1,W1. L1 = K1.ⓑ{J1}W1 → 0 < d → +fact lsuby_inv_succ1_aux: ∀L1,L2,l,m. L1 ⊆[l, m] L2 → + ∀J1,K1,W1. L1 = K1.ⓑ{J1}W1 → 0 < l → L2 = ⋆ ∨ - ∃∃J2,K2,W2. K1 ⊆[⫰d, e] K2 & L2 = K2.ⓑ{J2}W2. -#L1 #L2 #d #e * -L1 -L2 -d -e /2 width=1 by or_introl/ + ∃∃J2,K2,W2. K1 ⊆[⫰l, m] K2 & L2 = K2.ⓑ{J2}W2. +#L1 #L2 #l #m * -L1 -L2 -l -m /2 width=1 by or_introl/ [ #I1 #I2 #L1 #L2 #V1 #V2 #_ #J1 #K1 #W1 #_ #H elim (ylt_yle_false … H) // -| #I1 #I2 #L1 #L2 #V #e #_ #J1 #K1 #W1 #_ #H +| #I1 #I2 #L1 #L2 #V #m #_ #J1 #K1 #W1 #_ #H elim (ylt_yle_false … H) // -| #I1 #I2 #L1 #L2 #V1 #V2 #d #e #HL12 #J1 #K1 #W1 #H #_ destruct +| #I1 #I2 #L1 #L2 #V1 #V2 #l #m #HL12 #J1 #K1 #W1 #H #_ destruct /3 width=5 by ex2_3_intro, or_intror/ ] qed-. -lemma lsuby_inv_succ1: ∀I1,K1,L2,V1,d,e. K1.ⓑ{I1}V1 ⊆[d, e] L2 → 0 < d → +lemma lsuby_inv_succ1: ∀I1,K1,L2,V1,l,m. K1.ⓑ{I1}V1 ⊆[l, m] L2 → 0 < l → L2 = ⋆ ∨ - ∃∃I2,K2,V2. K1 ⊆[⫰d, e] K2 & L2 = K2.ⓑ{I2}V2. + ∃∃I2,K2,V2. K1 ⊆[⫰l, m] K2 & L2 = K2.ⓑ{I2}V2. /2 width=5 by lsuby_inv_succ1_aux/ qed-. -fact lsuby_inv_zero2_aux: ∀L1,L2,d,e. L1 ⊆[d, e] L2 → - ∀J2,K2,W2. L2 = K2.ⓑ{J2}W2 → d = 0 → e = 0 → +fact lsuby_inv_zero2_aux: ∀L1,L2,l,m. L1 ⊆[l, m] L2 → + ∀J2,K2,W2. L2 = K2.ⓑ{J2}W2 → l = 0 → m = 0 → ∃∃J1,K1,W1. K1 ⊆[0, 0] K2 & L1 = K1.ⓑ{J1}W1. -#L1 #L2 #d #e * -L1 -L2 -d -e -[ #L1 #d #e #J2 #K2 #W1 #H destruct +#L1 #L2 #l #m * -L1 -L2 -l -m +[ #L1 #l #m #J2 #K2 #W1 #H destruct | #I1 #I2 #L1 #L2 #V1 #V2 #HL12 #J2 #K2 #W2 #H #_ #_ destruct /2 width=5 by ex2_3_intro/ -| #I1 #I2 #L1 #L2 #V #e #_ #J2 #K2 #W2 #_ #_ #H +| #I1 #I2 #L1 #L2 #V #m #_ #J2 #K2 #W2 #_ #_ #H elim (ysucc_inv_O_dx … H) -| #I1 #I2 #L1 #L2 #V1 #V2 #d #e #_ #J2 #K2 #W2 #_ #H +| #I1 #I2 #L1 #L2 #V1 #V2 #l #m #_ #J2 #K2 #W2 #_ #H elim (ysucc_inv_O_dx … H) ] qed-. @@ -165,72 +165,72 @@ lemma lsuby_inv_zero2: ∀I2,K2,L1,V2. L1 ⊆[0, 0] K2.ⓑ{I2}V2 → ∃∃I1,K1,V1. K1 ⊆[0, 0] K2 & L1 = K1.ⓑ{I1}V1. /2 width=9 by lsuby_inv_zero2_aux/ qed-. -fact lsuby_inv_pair2_aux: ∀L1,L2,d,e. L1 ⊆[d, e] L2 → - ∀J2,K2,W. L2 = K2.ⓑ{J2}W → d = 0 → 0 < e → - ∃∃J1,K1. K1 ⊆[0, ⫰e] K2 & L1 = K1.ⓑ{J1}W. -#L1 #L2 #d #e * -L1 -L2 -d -e -[ #L1 #d #e #J2 #K2 #W #H destruct +fact lsuby_inv_pair2_aux: ∀L1,L2,l,m. L1 ⊆[l, m] L2 → + ∀J2,K2,W. L2 = K2.ⓑ{J2}W → l = 0 → 0 < m → + ∃∃J1,K1. K1 ⊆[0, ⫰m] K2 & L1 = K1.ⓑ{J1}W. +#L1 #L2 #l #m * -L1 -L2 -l -m +[ #L1 #l #m #J2 #K2 #W #H destruct | #I1 #I2 #L1 #L2 #V1 #V2 #_ #J2 #K2 #W #_ #_ #H elim (ylt_yle_false … H) // -| #I1 #I2 #L1 #L2 #V #e #HL12 #J2 #K2 #W #H #_ #_ destruct +| #I1 #I2 #L1 #L2 #V #m #HL12 #J2 #K2 #W #H #_ #_ destruct /2 width=4 by ex2_2_intro/ -| #I1 #I2 #L1 #L2 #V1 #V2 #d #e #_ #J2 #K2 #W #_ #H +| #I1 #I2 #L1 #L2 #V1 #V2 #l #m #_ #J2 #K2 #W #_ #H elim (ysucc_inv_O_dx … H) ] qed-. -lemma lsuby_inv_pair2: ∀I2,K2,L1,V,e. L1 ⊆[0, e] K2.ⓑ{I2}V → 0 < e → - ∃∃I1,K1. K1 ⊆[0, ⫰e] K2 & L1 = K1.ⓑ{I1}V. +lemma lsuby_inv_pair2: ∀I2,K2,L1,V,m. L1 ⊆[0, m] K2.ⓑ{I2}V → 0 < m → + ∃∃I1,K1. K1 ⊆[0, ⫰m] K2 & L1 = K1.ⓑ{I1}V. /2 width=6 by lsuby_inv_pair2_aux/ qed-. -fact lsuby_inv_succ2_aux: ∀L1,L2,d,e. L1 ⊆[d, e] L2 → - ∀J2,K2,W2. L2 = K2.ⓑ{J2}W2 → 0 < d → - ∃∃J1,K1,W1. K1 ⊆[⫰d, e] K2 & L1 = K1.ⓑ{J1}W1. -#L1 #L2 #d #e * -L1 -L2 -d -e -[ #L1 #d #e #J2 #K2 #W2 #H destruct +fact lsuby_inv_succ2_aux: ∀L1,L2,l,m. L1 ⊆[l, m] L2 → + ∀J2,K2,W2. L2 = K2.ⓑ{J2}W2 → 0 < l → + ∃∃J1,K1,W1. K1 ⊆[⫰l, m] K2 & L1 = K1.ⓑ{J1}W1. +#L1 #L2 #l #m * -L1 -L2 -l -m +[ #L1 #l #m #J2 #K2 #W2 #H destruct | #I1 #I2 #L1 #L2 #V1 #V2 #_ #J2 #K2 #W2 #_ #H elim (ylt_yle_false … H) // -| #I1 #I2 #L1 #L2 #V #e #_ #J2 #K1 #W2 #_ #H +| #I1 #I2 #L1 #L2 #V #m #_ #J2 #K1 #W2 #_ #H elim (ylt_yle_false … H) // -| #I1 #I2 #L1 #L2 #V1 #V2 #d #e #HL12 #J2 #K2 #W2 #H #_ destruct +| #I1 #I2 #L1 #L2 #V1 #V2 #l #m #HL12 #J2 #K2 #W2 #H #_ destruct /2 width=5 by ex2_3_intro/ ] qed-. -lemma lsuby_inv_succ2: ∀I2,K2,L1,V2,d,e. L1 ⊆[d, e] K2.ⓑ{I2}V2 → 0 < d → - ∃∃I1,K1,V1. K1 ⊆[⫰d, e] K2 & L1 = K1.ⓑ{I1}V1. +lemma lsuby_inv_succ2: ∀I2,K2,L1,V2,l,m. L1 ⊆[l, m] K2.ⓑ{I2}V2 → 0 < l → + ∃∃I1,K1,V1. K1 ⊆[⫰l, m] K2 & L1 = K1.ⓑ{I1}V1. /2 width=5 by lsuby_inv_succ2_aux/ qed-. (* Basic forward lemmas *****************************************************) -lemma lsuby_fwd_length: ∀L1,L2,d,e. L1 ⊆[d, e] L2 → |L2| ≤ |L1|. -#L1 #L2 #d #e #H elim H -L1 -L2 -d -e normalize /2 width=1 by le_S_S/ +lemma lsuby_fwd_length: ∀L1,L2,l,m. L1 ⊆[l, m] L2 → |L2| ≤ |L1|. +#L1 #L2 #l #m #H elim H -L1 -L2 -l -m normalize /2 width=1 by le_S_S/ qed-. (* Properties on basic slicing **********************************************) -lemma lsuby_drop_trans_be: ∀L1,L2,d,e. L1 ⊆[d, e] L2 → +lemma lsuby_drop_trans_be: ∀L1,L2,l,m. L1 ⊆[l, m] L2 → ∀I2,K2,W,s,i. ⬇[s, 0, i] L2 ≡ K2.ⓑ{I2}W → - d ≤ i → i < d + e → - ∃∃I1,K1. K1 ⊆[0, ⫰(d+e-i)] K2 & ⬇[s, 0, i] L1 ≡ K1.ⓑ{I1}W. -#L1 #L2 #d #e #H elim H -L1 -L2 -d -e -[ #L1 #d #e #J2 #K2 #W #s #i #H + l ≤ i → i < l + m → + ∃∃I1,K1. K1 ⊆[0, ⫰(l+m-i)] K2 & ⬇[s, 0, i] L1 ≡ K1.ⓑ{I1}W. +#L1 #L2 #l #m #H elim H -L1 -L2 -l -m +[ #L1 #l #m #J2 #K2 #W #s #i #H elim (drop_inv_atom1 … H) -H #H destruct | #I1 #I2 #L1 #L2 #V1 #V2 #_ #_ #J2 #K2 #W #s #i #_ #_ #H elim (ylt_yle_false … H) // -| #I1 #I2 #L1 #L2 #V #e #HL12 #IHL12 #J2 #K2 #W #s #i #H #_ >yplus_O1 +| #I1 #I2 #L1 #L2 #V #m #HL12 #IHL12 #J2 #K2 #W #s #i #H #_ >yplus_O1 elim (drop_inv_O1_pair1 … H) -H * #Hi #HLK1 [ -IHL12 | -HL12 ] [ #_ destruct -I2 >ypred_succ /2 width=4 by drop_pair, ex2_2_intro/ | lapply (ylt_inv_O1 i ?) /2 width=1 by ylt_inj/ #H yminus_succ yplus_succ1 #H lapply (ylt_inv_succ … H) -H - #Hide lapply (drop_inv_drop1_lt … HLK2 ?) -HLK2 /2 width=1 by ylt_O/ +| #I1 #I2 #L1 #L2 #V1 #V2 #l #m #_ #IHL12 #J2 #K2 #W #s #i #HLK2 #Hli + elim (yle_inv_succ1 … Hli) -Hli + #Hli #Hi yplus_succ1 #H lapply (ylt_inv_succ … H) -H + #Hilm lapply (drop_inv_drop1_lt … HLK2 ?) -HLK2 /2 width=1 by ylt_O/ #HLK1 elim (IHL12 … HLK1) -IHL12 -HLK1 yminus_SO2 /4 width=4 by ylt_O, drop_drop_lt, ex2_2_intro/ ]