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Putnam
1970 Putnam
B3
B3
Part of
1970 Putnam
Problems
(1)
Putnam 1970 B3
Source: Putnam 1970
5/17/2022
A closed subset
S
S
S
of
R
2
\mathbb{R}^{2}
R
2
lies in
a
<
x
<
b
a<x<b
a
<
x
<
b
. Show that its projection on the
y
y
y
-axis is closed.
Putnam
general topology
closed set