leanprover-community / leanprover-community/mathlib4
Define the setoid that glues a set into a pt
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Description
Add a setoid with relation given by (x ∈ s ∧ y ∈ s) ∨ x = y and
prove basic properties.
Motivation: quotients of this type are common in counterexamples in
topology.
See also Zulip chat
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
No file or test entry point is specified. Search the library for existing setoid and quotient definitions, then formalize the stated relation and its basic properties; the work is done when the new definition and proofs compile.
Written by the indexing model from the issue text.
Assessment
- Domain
- tooling
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100