7ccdfc30ff
Per request on [zulip](https://leanprover.zulipchat.com/#narrow/channel/270676-lean4/topic/apply.3F.20using.20tombstones/near/482895588).
37 lines
969 B
Text
37 lines
969 B
Text
/-!
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# Issue 3922
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The `apply?` tactic would apply `symm` to every hypothesis in the local context,
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leading to these new hypotheses being included in the term even if they weren't used.
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They also created unelaboratable terms such as `?_ (id (r.symm h₂))`.
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-/
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set_option linter.unusedVariables false
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-- set up a binary relation
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axiom r : Nat → Nat → Prop
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-- that is symmetric
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axiom r.symm {a b : Nat} : r a b → r b a
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-- and has some other property
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axiom r.trans {a b c : Nat} : r a b → r b c → r a c
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/--
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info: Try this: refine r.symm ?_
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---
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info: Try this: refine r.trans ?_ ?_
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---
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warning: declaration uses 'sorry'
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-/
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#guard_msgs (ordering := sorted) in
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example (a b c : Nat) (h₁ : r b a) (h₂ : r b c) : r c a := by
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apply?
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-- now attach the `symm` attribute to `r.symm`
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attribute [symm] r.symm
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/-- info: Try this: exact r.trans (id (r.symm h₂)) h₁ -/
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#guard_msgs in
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example (a b c : Nat) (h₁ : r b a) (h₂ : r b c) : r c a := by
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apply?
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