When you cut something with a knife, does the blade come into contact with each of the little pieces? I think so.
Now consider a topological version of this question. Let be a connected topological space (with more than 1 point) which we “cut” by removing a point
. Let
be a connected component of
; this is one of the little pieces. Is it true that
?
True if we replace “connected” by “path-connected”. Indeed, let be a continuous function such that
and
. If necessary, we truncate
so that
for
. Now the set
is a path-connected subset of
, hence
. Since
as
, we have
.
False as stated, even if is a subset of
. Here is a counterexample given by Niels Diepeveen on Math.StackExchange:
The set consists of the point
and of closed line segments from
to
. The union of line segments is connected, and since it is dense in
,
is also connected. However, once
is removed, each line segment becomes its own connected component, and so does the point
. Clearly, the closure of
does not contain
.
In this example is not compact. It turns out that the statement is true when
is a compact connected Hausdorff space (i.e., a continuum), but the proof (also given by Niels Diepeveen) is not easy.






Have you heard of the Knaster-Kuratowski fan? It is a connected subset of the plane that becomes totally disconnected upon removal of a certain point. So the knife doesn’t touch any of the pieces that remain.
That’s a more impressive example, of course — but clearly beyond my ability to draw…