diff --git a/properties/P000230.md b/properties/P000230.md new file mode 100644 index 000000000..c33916d4d --- /dev/null +++ b/properties/P000230.md @@ -0,0 +1,17 @@ +--- +uid: P000230 +name: Locally simply connected +refs: + - zb: "1209.57001" + name: Introduction to topological manifolds (Lee) + - mo: 487326 + name: 'Definition of locally simply connected space' + - zb: "1030.57035" + name: Bing's dogbone space is not strongly locally simply connected +--- + +$X$ admits a basis of open sets which are {P200}. + +Equivalently, for each $x \in X$, every neighborhood of $x$ contains a simply connected open neighborhood of $x$. + +Defined on page 298 of {{zb:1209.57001}}, page 495 of {{zb:0951.54001}} and as property $P_1$ of {{mo:487326}}. Has also been called "strongly locally simply connected", for example in {{zb:1030.57035}}. diff --git a/properties/P000231.md b/properties/P000231.md new file mode 100644 index 000000000..2c7f69a5f --- /dev/null +++ b/properties/P000231.md @@ -0,0 +1,13 @@ +--- +uid: P000231 +name: Weakly locally simply connected +refs: + - zb: "0063.00842" + name: Theory of Lie groups. I (Chevalley) + - mo: 487326 + name: 'Definition of locally simply connected space' +--- + +Every point of $X$ has a neighborhood which is {P200}. + +Defined as "locally simply connected" on page 54 of {{zb:0063.00842}} and as property $P_4$ of {{mo:487326}}. diff --git a/properties/P000232.md b/properties/P000232.md new file mode 100644 index 000000000..d3a48dd89 --- /dev/null +++ b/properties/P000232.md @@ -0,0 +1,27 @@ +--- +uid: P000232 +name: $LC^1$ +aliases: + - Locally simply connected +refs: + - zb: "0153.52905" + name: Theory of retracts (Borsuk) + - mo: 487326 + name: 'Definition of locally simply connected space' + - mathse: 5126526 + name: Is Borsuk's definition of $LC^1$ equivalent to this formulation of 'locally simply connected' ($P_{10}$)? + - zb: "0198.56303" + name: Acyclicity in three-manifolds +--- + +$X$ is locally $0$-connected and locally $1$-connected, as in {{zb:0153.52905}}. +A space $X$ is locally $n$-connected if for every $x \in X$ and each neighborhood $N$ of $x$ in $X$, there is a neighborhood $U$ of $x$ contained in $N$ such that every map $S^n \to N$ with values in $U$ is null-homotopic in $N$. + +Equivalently, for each $x \in X$, every neighborhood $N$ of $x$ contains a {P37} neighborhood $U$ of $x$ such that every loop $\phi:S^1\to U$ is null-homotopic in $N$. See {{mathse:5126526}}. + +This property is part of a hierarchy of $LC^n$ properties which includes {P42} as $LC^0$. +Defined on page 54 of {{zb:0153.52905}} and as property $P_{10}$ of {{mo:487326}}. Has also been called "locally simply connected", for example in {{zb:0198.56303}}. + +---- +#### Meta-properties +- This property is preserved by retractions. diff --git a/theorems/T000847.md b/theorems/T000847.md index 1c68ff60f..131e5ba0e 100644 --- a/theorems/T000847.md +++ b/theorems/T000847.md @@ -3,11 +3,12 @@ uid: T000847 if: P000122: true then: - P000229: true + P000230: true refs: - zb: "0951.54001" name: Topology (Munkres) --- -For $x \in X$ pick a neighborhood $U$ homeomorphic to $\mathbb{R}^n$. -Then $\pi_1(U,x)$ is trivial (see Example 1 on page 331 of {{zb:0951.54001}}). +A locally Euclidean space admits a basis of Euclidean open balls. +For a Euclidean open ball $U$ and $x \in U$, $\pi_1(U,x)$ is trivial (see Example 1 on page 331 of {{zb:0951.54001}}). +The claim follows because $\mathbb{R}^n$ is contractible, and {T583}. diff --git a/theorems/T000848.md b/theorems/T000848.md index 93c4720bb..3ef87964f 100644 --- a/theorems/T000848.md +++ b/theorems/T000848.md @@ -3,7 +3,7 @@ uid: T000848 if: P000090: true then: - P000229: true + P000230: true refs: - mathse: 2965374 name: Answer to "Are minimal neighborhoods in an Alexandrov topology path-connected?" diff --git a/theorems/T000853.md b/theorems/T000853.md new file mode 100644 index 000000000..e6b957eec --- /dev/null +++ b/theorems/T000853.md @@ -0,0 +1,9 @@ +--- +uid: T000853 +if: + P000230: true +then: + P000231: true +--- + +Immediate from the definitions. diff --git a/theorems/T000854.md b/theorems/T000854.md new file mode 100644 index 000000000..f7b145bcf --- /dev/null +++ b/theorems/T000854.md @@ -0,0 +1,9 @@ +--- +uid: T000854 +if: + P000230: true +then: + P000232: true +--- + +Immediate from the equivalent characterizations of each property. diff --git a/theorems/T000855.md b/theorems/T000855.md new file mode 100644 index 000000000..8dbd02379 --- /dev/null +++ b/theorems/T000855.md @@ -0,0 +1,9 @@ +--- +uid: T000855 +if: + P000231: true +then: + P000229: true +--- + +Immediate from the definitions. diff --git a/theorems/T000856.md b/theorems/T000856.md new file mode 100644 index 000000000..d681b476c --- /dev/null +++ b/theorems/T000856.md @@ -0,0 +1,17 @@ +--- +uid: T000856 +if: + P000232: true +then: + P000229: true +refs: +- mathse: 4044399 + name: Characterizing simply connected spaces +--- + +Let $x \in X$. By {P232}, there exists a path-connected neighborhood $U$ of $x$ such that every +loop $ S^1 \to X$ loop with image in $U$ is null-homotopic. Let $\sigma$ be a loop in $U$ based at $x$. +Choose a null-homotopy $F : S^1 \times [0, 1] \to X$ from $\sigma$ to a constant loop. Apply the arguments +$(4) \Rightarrow (5)$ and $(5) \Rightarrow (1)$ from {{mathse:4044399}} to $F$ in order to construct a +basepoint preserving null-homotopy of $\sigma$ to the constant loop at $x$. +Then {P229} follows. diff --git a/theorems/T000857.md b/theorems/T000857.md new file mode 100644 index 000000000..a3df3fa5c --- /dev/null +++ b/theorems/T000857.md @@ -0,0 +1,9 @@ +--- +uid: T000857 +if: + P000232: true +then: + P000042: true +--- + +$LC^1$ implies $LC^0$ by definition.