2 added 4 characters in body edited Oct 10 '13 at 3:17 Zev Chonoles 112k77 gold badges3737 silver badges8888 bronze badges The commands \lbrack and \rbrack are macros that produce [ and ] respectively, and MathJax has no problem when you use them instead of the symbols (see- see the comment below), which was produced by For any $$a,b\in \lbrack 0,x)$$: $$a\vee b$$ exists. Namely, $$a\vee b=\max\{a,b\}$$. You might be asking about when directed sets are [complete](http://en.wikipedia.org/wiki/Complete_partial_order)?  Incidentally, note that you should use \max instead of just max to produce a math operator. The commands \lbrack and \rbrack are macros that produce [ and ] respectively, and MathJax has no problem when you use them instead of the symbols (see comment below), which was produced by For any $$a,b\in \lbrack 0,x)$$: $$a\vee b$$ exists. Namely, $$a\vee b=\max\{a,b\}$$. You might be asking about when directed sets are [complete](http://en.wikipedia.org/wiki/Complete_partial_order)?  Incidentally, note that you should use \max instead of just max to produce a math operator. The commands \lbrack and \rbrack are macros that produce [ and ] respectively, and MathJax has no problem when you use them instead of the symbols - see the comment below, which was produced by For any $$a,b\in \lbrack 0,x)$$: $$a\vee b$$ exists. Namely, $$a\vee b=\max\{a,b\}$$. You might be asking about when directed sets are [complete](http://en.wikipedia.org/wiki/Complete_partial_order)?  Incidentally, note that you should use \max instead of just max to produce a math operator. 1 answered Oct 10 '13 at 3:06 Zev Chonoles 112k77 gold badges3737 silver badges8888 bronze badges The commands \lbrack and \rbrack are macros that produce [ and ] respectively, and MathJax has no problem when you use them instead of the symbols (see comment below), which was produced by For any $$a,b\in \lbrack 0,x)$$: $$a\vee b$$ exists. Namely, $$a\vee b=\max\{a,b\}$$. You might be asking about when directed sets are [complete](http://en.wikipedia.org/wiki/Complete_partial_order)?  Incidentally, note that you should use \max instead of just max to produce a math operator.