Hello Andrey,

I would suggest to change the assignment operator ( := ) behavior. Just look at this, please:
[MATH]x←5+6[/MATH]
[MATH]x=5[/MATH] WRONG!
This is because we can type something like this:

x:5[SPACE]+6

This can be hard to trace. Fortunately, we can put the mouse on the region and see the probem, if the expression is simple. If the expression is a bit more complicated we might not see where the problem was. Just a single careless [SPACE] might make a problem.

I suggest (if possible) not to allow inserting anything when, say, this is the case:

Inserting any operator, or anything else should be simply disabled.

Regards,
Radovan