We all know how terrible Marx's understanding of economics was, but how many people knew that he was a terrible mathematician, as well? Here, behold this genius trying to define 0/0:

https://www.researchgate.net/publication/255609552_Calculus_A_Marxist_approach

"In calculating the derivative of a function from first principles, Marx did not like the notion of a limit. When considering (f(x) − f(a))/(x − a) he wanted to put x = a, after suitable cancelling or some other algebraic simplification, and write the result as 0/0. He did not see 0/0 as a fraction; he saw it as one symbol."

For those who don't know, 0/0 is undefined because it literally can't have any consistent definition. So this is equivalent to starting your reasoning with a premise like x and not x, which would imply, insensibly, that everything is true.

As Wikipedia puts it, if b ≠ 0 then the equation a/b = c is equivalent to a = b × c. Assuming that a/0 is a number c, then it must be that a = 0 × c = 0. However, the single number c would then have to be determined by the equation 0 = 0 × c, but every number satisfies this equation, so we cannot assign a numerical value to 0/0.

https://en.wikipedia.org/wiki/Division_by_zero

Weird how they ... somehow forgot ... to mention that in his list of math publications, though:

https://en.wikipedia.org/wiki/Mathematical_manuscripts_of_Karl_Marx?wprov=sfla1

So if any of you are unfortunate enough to know Marx bros, you can point out that he was a terrible mathematician as well as a terrible economist.