10 lines
201 B
Text
10 lines
201 B
Text
import logic
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theorem tst (a b : Prop) (H : a ↔ b) : b ↔ a
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:= by apply iff.intro;
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intro Hb;
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apply (iff.elim_right H Hb);
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intro Ha;
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apply (iff.elim_left H Ha)
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check tst
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