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If two spaces have the same sets, then the spaces restricted to the same set have the same sets. |
The sets of a countable space restricted to a subset are the same as the sets of the countable space restricted to the intersection of the subset with the original space. |
The sets of a space restricted to the whole space are the same as the sets of the original space. |
The sets of a space restricted to a subset $A$ and then restricted to a subset $B$ are the same as the sets of the space restricted to the intersection of $A$ and $B$. |
If $\Omega$ is a measurable set, then a set $A$ is measurable with respect to the restriction of the measure space $M$ to $\Omega$ if and only if $A$ is a subset of $\Omega$ and is measurable with respect to $M$. |
If two measurable spaces have the same sets, then the restrictions of those spaces to the same set have the same sets. |
If $\Omega$ is a subset of the sample space of a measure space $M$, then the $\sigma$-algebra of the restricted measure space $M|\Omega$ is equal to the $\sigma$-algebra of the preimage measure space $\Omega \times M$ under the projection map $\pi: \Omega \times M \to M$. |
If $S$ is a measurable set, then the set $\{x \in S : P(x)\}$ is measurable if and only if the set $\{x \in X : x \in S \text{ and } P(x)\}$ is measurable. |
If $f$ is a measurable function from $M$ to $N$, then $f$ is a measurable function from $M \cap \Omega$ to $N$. |
A function $f$ is measurable with respect to the restriction of a measure space $N$ to a set $\Omega$ if and only if $f$ is measurable with respect to $N$ and $f$ is a function from the space of $M$ to $\Omega$. |
If $f$ is a measurable function from a measure space $M$ to a measure space $N$, then the restriction of $f$ to a subset $\Omega$ of $N$ is a measurable function from $M$ to the measure space $N$ restricted to $\Omega$. |
If $f$ is measurable on each of a countable collection of sets whose union is the whole space, then $f$ is measurable on the whole space. |
If $f$ is a measurable function from a measurable space $M$ to a measurable space $N$, then $f$ is measurable on each measurable subset of $M$. |
If $P$ is a measurable predicate, then the function $f$ is measurable if and only if the restrictions of $f$ to the sets $\{x \in X : P(x)\}$ and $\{x \in X : \lnot P(x)\}$ are measurable. |
If $f$ and $g$ are measurable functions from $M$ to $M'$, and $P$ is a measurable predicate on $M$, then the function $h$ defined by $h(x) = f(x)$ if $P(x)$ is true, and $h(x) = g(x)$ if $P(x)$ is false, is measurable. |
If $f$ and $g$ are measurable functions from a measure space $M$ to a measure space $M'$, and $A$ is a measurable subset of $M$, then the function $h$ defined by $h(x) = f(x)$ if $x \<in> A$ and $h(x) = g(x)$ if $x \<notin> A$ is measurable. |
If $\Omega$ is a measurable subset of the space of a measure $M$, and $c$ is an element of the space of a measure $N$, then a function $f$ is measurable from the restriction of $M$ to $\Omega$ to $N$ if and only if the function $x \mapsto f(x)$ if $x \in \Omega$ and $c$ otherwise is measurable from $M$ to $N$. |
If $x$ is an element of the underlying set of a measure space $M$, then the measure space $M$ restricted to the singleton set $\{x\}$ is isomorphic to the measure space $\{x\}$ with the counting measure. |
If $f$ is a measurable function from a space $M$ to a space $N$ and $X$ is a countable subset of $M$, then $f$ is also measurable when restricted to $M \setminus X$. |
If $f$ is a measurable function from a measurable space $M$ to a measurable space $N$, and $X$ is a countable subset of $M$ such that $f$ and $g$ agree on $M \setminus X$, then $g$ is measurable. |
If $f$ is a measurable function from a measure space $M$ to a countable set $A$, and $A$ is a subset of a countable set $B$, then $f$ is a measurable function from $M$ to $B$. |
If $f$ is a sequence of complex numbers and $z$ is a complex number, then $\limsup_{n \to \infty} \sqrt[n]{|f_n z^n|} = \limsup_{n \to \infty} \sqrt[n]{|f_n|} |z|$. |
If the sequence $(\sqrt[n]{\|f_n\|})$ converges to $l$, then the limit superior of the sequence is also $l$. |
If $\lim_{n \to \infty} \sqrt[n]{|f_n|} = l$, then $\limsup_{n \to \infty} \sqrt[n]{|f_n|} = l$. |
If the root test converges, then the series converges. |
If the root test for a series $\sum a_n$ gives a limit superior greater than 1, then the series diverges. |
The empty set is open. |
The union of two open sets is open. |
If $B_x$ is open for all $x \in A$, then $\bigcup_{x \in A} B_x$ is open. |
If $S$ is a finite set of open sets, then $\bigcap S$ is open. |
If $A$ is a finite set and each $B_x$ is open, then $\bigcap_{x \in A} B_x$ is open. |
If every point in a set $S$ has an open neighborhood contained in $S$, then $S$ is open. |
A set is open if and only if every point in the set is contained in an open set that is contained in the set. |
The empty set is closed. |
The union of two closed sets is closed. |
The whole space is closed. |
The intersection of two closed sets is closed. |
If $B_x$ is closed for all $x \in A$, then $\bigcap_{x \in A} B_x$ is closed. |
The intersection of a collection of closed sets is closed. |
The union of a finite collection of closed sets is closed. |
The union of a finite collection of closed sets is closed. |
A set is open if and only if its complement is closed. |
A set $S$ is closed if and only if its complement $-S$ is open. |
If $S$ is open and $T$ is closed, then $S - T$ is open. |
If $S$ is closed and $T$ is open, then $S - T$ is closed. |
The complement of a closed set is open. |
The complement of an open set is closed. |
If a set is closed, then its complement is open. |
If $P$ and $Q$ are open sets, then $P \cap Q$ is an open set. |
If $P$ and $Q$ are open sets, then $P \cup Q$ is an open set. |
If each set $\{x \mid P_i(x)\}$ is open, then so is the set $\{x \mid \exists i. P_i(x)\}$. |
If $P$ is closed and $Q$ is open, then the set of points $x$ such that $P(x) \implies Q(x)$ is open. |
The set of all $x$ such that $P$ is open. |
If the set of points $x$ such that $P(x)$ is true is open, then the set of points $x$ such that $P(x)$ is false is closed. |
The intersection of two closed sets is closed. |
If $P$ and $Q$ are closed sets, then $P \cup Q$ is closed. |
If $P_i$ is a closed set for each $i$, then $\{x \mid \forall i. P_i(x)\}$ is closed. |
If the set of points $x$ such that $P(x)$ is true is open, and the set of points $x$ such that $Q(x)$ is true is closed, then the set of points $x$ such that $P(x) \implies Q(x)$ is true is closed. |
The set of all $x$ such that $P$ is closed. |
Two points $x$ and $y$ are distinct if and only if there exists an open set $U$ such that $x \in U$ and $y \notin U$. |
The singleton set $\{a\}$ is closed. |
If $S$ is a closed set, then $S \cup \{a\}$ is closed. |
If $S$ is a finite set, then $S$ is closed. |
In a $T_2$ space, two points are distinct if and only if there exist disjoint open sets containing them. |
In a $T_0$ space, two points are distinct if and only if there is an open set that contains one of them but not the other. |
In a perfect space, the whole space is not a singleton. |
If $K_i$ generates the topology on $S$ for each $i \in I$, then $\bigcup_{i \in I} K_i$ generates the topology on $S$. |
The topology generated by a set of subsets of a set is a topology. |
The set of all real numbers greater than $a$ is open. |
The set $\{x \in \mathbb{R} \mid x < a\}$ is open. |
The set of real numbers between $a$ and $b$ is open. |
The set $\{x \in \mathbb{R} \mid x \leq a\}$ is closed. |
The set $\{x \in \mathbb{R} \mid x \geq a\}$ is closed. |
The closed interval $[a, b]$ is closed. |
If $x < y$ in a totally ordered set, then there exist $a$ and $b$ such that $x \in (-\infty, a)$, $y \in (b, \infty)$, and $(-\infty, a) \cap (b, \infty) = \emptyset$. |
If $S$ is an open set in a linearly ordered topology, and $x \in S$, then there exists a point $b > x$ such that the interval $(x, b)$ is contained in $S$. |
If $S$ is an open set in a linearly ordered topology, and $x \in S$, then there exists a point $b < x$ such that the interval $(b, x)$ is contained in $S$. |
If the open sets of a topological space are generated by a set $T$ of subsets, then the neighborhood filter of a point $x$ is the intersection of all sets in $T$ that contain $x$. |
A predicate $P$ holds eventually in the neighborhood filter of $a$ if and only if there exists an open set $S$ containing $a$ such that $P$ holds for all $x \in S$. |
For any point $x$ and any property $P$, the set of points $y$ such that $P$ holds in a neighborhood of $y$ is a neighborhood of $x$ if and only if $P$ holds in a neighborhood of $x$. |
If $s$ is an open set containing $x$, then there is a neighborhood of $x$ contained in $s$. |
If a property $P$ holds in a neighborhood of $x$, then $P$ holds at $x$. |
The neighborhood filter of a point in a topological space is never empty. |
If $x \neq y$, then for every open neighborhood $U$ of $x$, there exists an open neighborhood $V$ of $x$ such that $V \subseteq U$ and $V \cap \{y\} = \emptyset$. |
If $x$ is an isolated point, then the neighborhood filter of $x$ is the principal filter generated by $x$. |
In a discrete topology, the neighborhood of a point is the singleton set containing that point. |
In a discrete topology, the filter of neighborhoods of a point is the empty filter. |
In a discrete topology, a function $f$ converges to $y$ if and only if $f$ eventually equals $y$. |
The filter at $x$ within $s$ is the intersection of all open sets containing $x$ that are contained in $s$. |
If $P$ holds eventually at $a$ within $s$, then $P$ holds eventually in a neighborhood of $a$ if $x \neq a$ and $x \in s$. |
If $s \subseteq t$, then the filter of neighborhoods of $x$ in $s$ is finer than the filter of neighborhoods of $x$ in $t$. |
If $P$ holds eventually at $a$ within $s$, then there exists an open set $S$ containing $a$ such that $P$ holds for all $x \in S$ with $x \neq a$ and $x \in s$. |
If $a$ is in an open set $S$, then the filter of neighbourhoods of $a$ within $S$ is the same as the filter of neighbourhoods of $a$. |
If $a$ is in an open set $s$ and $s$ is disjoint from the complement of $s$, then the filter of neighbourhoods of $a$ within $s$ is the same as the filter of neighbourhoods of $a$. |
If $a$ is in an open subset $S$ of a topological space $T$, then the filter of neighbourhoods of $a$ within $T$ is the same as the filter of neighbourhoods of $a$ in $S$. |
If $x$ is in a set $S$ and $S$ is open, and if $T$ and $U$ are sets such that $T \cap S - \{x\} = U \cap S - \{x\}$, then the filter of neighborhoods of $x$ in $T$ is the same as the filter of neighborhoods of $x$ in $U$. |
The filter of neighbourhoods of a point $a$ in an empty set is the empty filter. |
The filter of neighbourhoods of $x$ in $S \cup T$ is the supremum of the filters of neighbourhoods of $x$ in $S$ and $T$. |
In a topological space, the filter at a point $a$ is the empty filter if and only if the singleton set $\{a\}$ is open. |
In a perfect space, the filter at a point is never the empty filter. |
Subsets and Splits