User blog comment:Boboris02/MBOT/@comment-30004975-20161219055116/@comment-1605058-20161220173427

And a question "What is +*^-/ ?" is a perfectly reasonable question, with a perfectly reasonable answer "It is not a correctly formed expression". And there is a reason why this is not a correctly formed expression - if we work in the language of arithmetic with the five symbols +, *, ^, -, / included, then "+*^-/" is not a well-formed formula according to the formation rules akin to the ones described in a link I gave in a comment above.

Also, you are still missing my point. I am not asking what \(\cup\Leftrightarrow\cup\) is. If we agree that it doesn't represent anything, then we have to exclude it from allowed expressions to be considered when interpreting MBOT. And the only way to exclude such "trash" formulas is to precisely describe which formulas aren't "trash", i.e. describe the grammar.