Papers
Topics
Authors
Recent
Search
2000 character limit reached

Returning functions with closed graph are continuous

Published 5 Mar 2019 in math.GN | (1903.01937v1)

Abstract: A function $f:X\to \mathbb R$ defined on a topological space $X$ is called returning if for any point $x\in X$ there exists a positive real number $M_x$ such that for every path-connected subset $C_x\subset X$ containing the point $x$ and any $y\in C_x\setminus{x}$ there exists a point $z\in C_x\setminus{x,y}$ such that $|f(z)|\le \max{M_x,|f(y)|}$. A topological space $X$ is called path-inductive if a subset $U\subset X$ is open if and only if for any path $\gamma:[0,1]\to X$ the preimage $\gamma{-1}(U)$ is open in $[0,1]$. The class of path-inductive spaces includes all first-countable locally path-connected spaces and all sequential locally contractible space. We prove that a function $f:X\to \mathbb R$ defined on a path-inductive space $X$ is continuous if and only of it is returning and has closed graph. This implies that a (weakly) \'Swi\c atkowski function $f:\mathbb R\to\mathbb R$ is continuous if and only if it has closed graph, which answers a problem of Maliszewski, inscibed to Lviv Scottish Book.

Summary

No one has generated a summary of this paper yet.

Paper to Video (Beta)

No one has generated a video about this paper yet.

Whiteboard

No one has generated a whiteboard explanation for this paper yet.

Open Problems

We haven't generated a list of open problems mentioned in this paper yet.

Continue Learning

We haven't generated follow-up questions for this paper yet.

Collections

Sign up for free to add this paper to one or more collections.