# Talk:Lower Set with no Greatest Element is Open in GO-Space

There are many ways to talk about open sets. A very common way is to identify the space with its underlying set, and just say "$x \in X$" or "$U$ is open in $X$". To be super-formal about it, you can either say "$U$ is open in $(X,\tau)$" or "$U \in \tau$". The former is clunky while the latter takes an extra translation step to read. If you have defined $T = (X, \tau)$ then you can say "open in $T$", but that's probably the worst of all, because it requires you to break out of your reading to go look up what the heck $T$ was. --Dfeuer (talk) 15:26, 23 February 2013 (UTC)