+(* LEMMA 3.57 *)
+
+lemma join_meet_le_join: ∀R.∀L:vlattice R.∀x,y,z:L.μ (x ∨ (y ∧ z)) ≤ μ (x ∨ z).
+intros (R L x y z);
+apply (le_rewl ??? ? (eq_sym ??? (step1_3_57' ?????)));
+apply (le_rewl ??? (μx+ μy+ μz+- μ(y∨z)+ -μ(z∧x∧y))); [
+ apply feq_plusl; apply feq_opp; apply (eq_trans ?? ? ?? (eq_sym ??? (meet_assoc ?????))); apply eq_reflexive;]
+apply (le_rewl ??? (μx+ μy+ μz+- μ(y∨z)+ (- ( μ(z∧x)+ μy+- μ((z∧x)∨y))))); [
+ apply feq_plusl; apply feq_opp; apply eq_sym; apply modularm]
+apply (le_rewl ??? (μx+ μy+ μz+- μ(y∨z)+ (- μ(z∧x)+ -μy+-- μ((z∧x)∨y)))); [
+ apply feq_plusl; apply (eq_trans ?? (- (μ(z∧x)+ μy) + -- μ((z∧x)∨y))); [
+ apply feq_plusr; apply eq_sym; apply eq_opp_plus_plus_opp_opp;]
+ apply eq_sym; apply eq_opp_plus_plus_opp_opp;]
+apply (le_rewl ??? (μx+ μy+ μz+- μ(y∨z)+(- μ(z∧x)+- μy+ μ(y∨(z∧x))))); [
+ repeat apply feq_plusl; apply eq_sym; apply (eq_trans ?? (μ((z∧x)∨y)) ? (eq_opp_opp_x_x ??));
+ apply join_comm;]
+apply (le_rewl ??? (μx+ μy+ μz+- μ(y∨z)+(- μ(z∧x)+- μy)+ μ(y∨(z∧x)))); [
+ apply eq_sym; apply plus_assoc;]
+apply (le_rewl ??? (μx+ μy+ μz+- μ(y∨z)+(- μy + - μ(z∧x))+ μ(y∨(z∧x)))); [
+ repeat apply feq_plusr; repeat apply feq_plusl; apply plus_comm;]
+apply (le_rewl ??? (μx+ μy+ μz+- μ(y∨z)+- μy + - μ(z∧x)+ μ(y∨(z∧x)))); [
+ repeat apply feq_plusr; apply eq_sym; apply plus_assoc;]
+apply (le_rewl ??? (μx+ μy+ μz+- μy + - μ(y∨z)+- μ(z∧x)+ μ(y∨(z∧x)))); [
+ repeat apply feq_plusr; apply (eq_trans ?? ? ?? (plus_assoc ????));
+ apply (eq_trans ?? ( μx+ μy+ μz+(- μy+- μ(y∨z))) ? (eq_sym ??? (plus_assoc ????)));
+ apply feq_plusl; apply plus_comm;]
+apply (le_rewl ??? (μx+ μy+ -μy+ μz + - μ(y∨z)+- μ(z∧x)+ μ(y∨(z∧x)))); [
+ repeat apply feq_plusr; apply (eq_trans ?? ? ?? (plus_assoc ????));
+ apply (eq_trans ?? (μx+ μy+( -μy+ μz)) ? (eq_sym ??? (plus_assoc ????)));
+ apply feq_plusl; apply plus_comm;]
+apply (le_rewl ??? (μx+ 0 + μz + - μ(y∨z)+- μ(z∧x)+ μ(y∨(z∧x)))); [
+ repeat apply feq_plusr; apply (eq_trans ?? ? ?? (plus_assoc ????));
+ apply feq_plusl; apply eq_sym; apply (eq_trans ?? ? ? (plus_comm ???));
+ apply opp_inverse; apply eq_reflexive;]
+apply (le_rewl ??? (μx+ μz + - μ(y∨z)+- μ(z∧x)+ μ(y∨(z∧x)))); [
+ repeat apply feq_plusr; apply (eq_trans ?? ? ?? (plus_comm ???));
+ apply eq_sym; apply zero_neutral;]
+apply (le_rewl ??? (μz+ μx + - μ(y∨z)+- μ(z∧x)+ μ(y∨(z∧x)))); [
+ repeat apply feq_plusr; apply plus_comm;]
+apply (le_rewl ??? (μz+ μx +- μ(z∧x)+ - μ(y∨z)+ μ(y∨(z∧x)))); [
+ repeat apply feq_plusr; apply (eq_trans ?? ? ?? (plus_assoc ????));
+ apply (eq_trans ?? ? ? (eq_sym ??? (plus_assoc ????))); apply feq_plusl;
+ apply plus_comm;]
+apply (le_rewl ??? (μ(z∨x)+ - μ(y∨z)+ μ(y∨(z∧x)))); [
+ repeat apply feq_plusr; apply modularj;]
+apply (le_rewl ??? (μ(z∨x)+ (- μ(y∨z)+ μ(y∨(z∧x)))) (plus_assoc ????));
+apply (le_rewr ??? (μ(x∨z) + 0)); [apply (eq_trans ?? ? ? (plus_comm ???)); apply zero_neutral]
+apply (le_rewr ??? (μ(x∨z) + (-μ(y∨z) + μ(y∨z)))); [ apply feq_plusl; apply opp_inverse]
+apply (le_rewr ??? (μ(z∨x) + (-μ(y∨z) + μ(y∨z)))); [ apply feq_plusr; apply join_comm;]
+repeat apply fle_plusl; apply join_meet_le;
+qed.
+
+lemma meet_le_meet_join: ∀R.∀L:vlattice R.∀x,y,z:L.μ (x ∧ z) ≤ μ (x ∧ (y ∨ z)).