i do not understand how this notation works.
help me please.
Hi, i don't know if the following visualisation is helpful:
but maybe this little proposition will make things clear:
Proof: "=>" assume for only finitely many , let be the biggest such , then for all we have . This means , so .
"<=" assume , this means there's some such that , that is, for all , so belongs to only finitely many .