--- a/agda/logic.agda	Thu Nov 07 10:55:22 2019 +0900
+++ b/agda/logic.agda	Thu Nov 07 11:36:23 2019 +0900
@@ -83,3 +83,23 @@
 bool-≡-? true false = no (λ ())
 bool-≡-? false true = no (λ ())
 bool-≡-? false false = yes refl
+
+¬-bool-t : {a : Bool} →  ¬ ( a ≡ true ) → a ≡ false
+¬-bool-t {true} ne = ⊥-elim ( ne refl )
+¬-bool-t {false} ne = refl
+
+¬-bool-f : {a : Bool} →  ¬ ( a ≡ false ) → a ≡ true
+¬-bool-f {true} ne = refl
+¬-bool-f {false} ne = ⊥-elim ( ne refl )
+
+lemma-∧-0 : {a b : Bool} → a /\ b ≡ true → a ≡ false → ⊥
+lemma-∧-0 {true} {true} refl ()
+lemma-∧-0 {true} {false} ()
+lemma-∧-0 {false} {true} ()
+lemma-∧-0 {false} {false} ()
+
+lemma-∧-1 : {a b : Bool} → a /\ b ≡ true → b ≡ false → ⊥
+lemma-∧-1 {true} {true} refl ()
+lemma-∧-1 {true} {false} ()
+lemma-∧-1 {false} {true} ()
+lemma-∧-1 {false} {false} ()