User blog comment:Boboris02/MBOT/@comment-30004975-20161219055116/@comment-1605058-20161220170310

\(\cup\Leftrightarrow\cup\) is a formula written using the symbols which you provide, hence I don't know what you mean by the fact that it "doesn't exist". Note I am not talking about any kind of meaning this formula has, but rather the formula itself.

What I suppose you might mean is that \(\cup\Leftrightarrow\cup\) is not a "proper" (or "correct", or "well-formed", however you want to call it) formula in the MBOT language. My question is then, why so? What are the rules which state what formulas are proper and which aren't? More figuratively, what is the "grammar" of MBOT language?