Some "forbidden" math facts. Just standard, random undergrad stuff really:
>there are as many rational numbers as natural numbers
>mathematicians haven't settled on whether 0 is natural or not
>in absolute generality, if a limit exists, it is not necessarily unique
>there can be "another" multiplication (comultiplication)
>the chance of randomly getting a rational number while picking a real number is 0. and I mean absolute zero, not 0.000...001.