[Merged by Bors] - chore(topology/separation): prove that {y | y ≠ x} is open
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src/topology/separation.lean
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| @@ -120,10 +120,12 @@ class t1_space (α : Type u) [topological_space α] : Prop := | |||
| lemma is_closed_singleton [t1_space α] {x : α} : is_closed ({x} : set α) := | |||
| t1_space.t1 x | |||
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| lemma is_open_ne [t1_space α] {x : α} : is_open {y | y ≠ x} := | |||
| by simpa using is_open_neg (t1_space.t1 x) | |||
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Was there a PR that changed the naming convention, so is_open_neg should now be is_open_compl?
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is_open_neg uses set_of. We also have is_open_compl_iff.
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After e8a68de is_open_neg is never used in mathlib.
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{y | y ≠ x} is open{y | y ≠ x} is open
anrddh
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