8 lines
213 B
Text
8 lines
213 B
Text
import logic
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exit -- TODO
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theorem tst (a b : Bool) (H : a ↔ b) : b ↔ a
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:= have H1 [fact] : a → b, from iff_elim_left H,
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by (apply iff_intro,
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assume Hb, iff_mp_right H Hb,
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assume Ha, H1 Ha)
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