Disjunctive sum
From Encyclopedia of Mathematics
disjunct sum, of topological spaces 
, 
The space 
, where each 
is a copy of 
and 
for 
, while the topology on 
is defined by the condition that a set 
is open in 
if and only if its intersection with each 
is open. In other words, each 
is open and closed in 
.
Comments
The space 
is also called the discrete sum or the discrete union of the 
.
How to Cite This Entry:
Disjunctive sum. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Disjunctive_sum&oldid=18973
Disjunctive sum. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Disjunctive_sum&oldid=18973
This article was adapted from an original article by A.A. Mal'tsev (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article