Alphabeta Math
TheoremStatement: Literature-sourcedProof: AI-adaptedprecheck passaudited 2026-08-16
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  • AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
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A space admitting a universal covering is semilocally simply connected

Statement

If a space admits a universal covering, then it is semilocally simply connected. No local path-connectedness hypothesis is required.

Facts & Assumptions

Given: The objects, hypotheses, and choice principles stated above.

[F1]

A universal covering space of B is a covering map p:B~→B whose total space B~ is simply connected (def-covering-map-and-evenly-covered-neighbourhoods, def-simply-connected). (Universal covering spaces).

[F2]

A space X is semilocally simply connected at x∈X when there is a neighbourhood U of x and a basepoint-preserving inclusion (U,x)↪(X,x) whose induced map on fundamental groups is trivial (def-neighbourhood-top, def-induced-homomorphism-on-fundamental-groups, def-based-loops-and-fundamental-group). It is semilocally simply connected when this holds at every point. The neighbourhood need not itself be simply connected. (Semilocally simply connected spaces with explicit basepoint convention).

[F3]

For a covering p:(E,e0)→(B,b0), the induced homomorphism p∗:π1(E,e0)→π1(B,b0) is injective. (A covering map induces an injective homomorphism on fundamental groups).

[F4]

A topological space X is simply connected when it is nonempty and path-connected (def-path-connected) and, for every x0∈X, the group π1(X,x0) has exactly one element. (Simply connected topological spaces).

Proof

technique · direct
1.1givenF2F1

At a basepoint choose an evenly covered neighbourhood and a lift of that point.

2.1step 1.1F2

Any loop in the neighbourhood lifts to a loop in its sheet.

3.1step 2.1F2F3F1

The induced fundamental-group map of the universal cover is injective and its domain group is trivial, so the inclusion-induced class downstairs is trivial.

4.1step 3.1F4F2

No local path-connectedness is needed for this necessity direction.

5.1step 4.1∎

The preceding construction and implications establish the assertion.

Depends on

Used by

Dependency tree · two levels

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Sources