> I can only assume that the definition of 'obscure' here refers to the vast majority of an mathematics undergraduate curriculum. Which is absurd. It's not abs

> I can only assume that the definition of 'obscure' here refers to the vast majority of an mathematics undergraduate curriculum. Which is absurd. It's not absurd at all. "Obscure" is relative to a given population. The relevant population here is not "mathematicians". The majority is indeed obscure to those outside the field. If you use "inside the field" you get absurdities such as homology being counted as not obscure. Calculus, and geometry are not obscure. Many non-mathematicians have heard of these, and some even use them. Both group theory and number theory are obscure. I say this as someone who uses the representation theory of groups regularly.