Difference finitely many and arbitrarily many

744 Views Asked by At

Is there a difference between "finitely many" and "arbitrarily many"? Some notes I am reading are making a point of distinguishing between the two and I thought they meant the same thing.

1

There are 1 best solutions below

2
On BEST ANSWER

"Arbitrarily many" can be infinite where "finitely many" cannot. A specific example is in topology, where the intersection of finitely many open sets is still open, while the union of arbitrarily many open sets is open. An example to show the infinite intersection of open sets may not be open comes from $\Bbb R$ with the usual topology. All the sets of the form $(-\frac 1n,\frac 1n)$ are open for $n \in \Bbb N$, and the intersection of finitely many of them is open, but the infinite intersection is $\{0\}$, which is not open.