9 lines
234 B
Text
9 lines
234 B
Text
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theorem symm_iff (p q : Bool) (H : p ↔ q) : (q ↔ p)
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:= symm H
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theorem or_imp (p q : Bool) : (p ∨ q) ↔ (¬ p → q)
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:= let H1 := symm_iff _ _ (imp_or (¬ p) q) in
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let H2 := not_not_eq p in
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let H3 := subst H1 H2 in
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H3
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