“Some characteristic C is what distinguishes A from B”

Question

In "some characteristic C is what distinguishes A from B", does characteristic C belongs to A but not to B, or to B but not to A?

For example:

Imposing restrictions on the available resources is what distinguishes computational complexity from computability theory.

Answer 1

It can be either A or undefined, but not B.

• Fiscal purism is what distinguishes her from other candidates. (A - she has fiscal purism)
• Reputation is what distinguishes one brand from another. (undefined)
• Obesity is what distinguishes my mother from yo momma. (even with clear context of The Dozens, it sounds as if the speaker is insulting his/her own mother)

Answer 2

it can probably go both ways and you can regard C as a discriminant

An expression used to distinguish or separate other expressions in a quantity or equation.

Answer 3

It depends on what the subject matter is. As the subject matter changes, (C) changes in distinguishing (A) or (B).
In your case, the fact that "imposing restrictions on the available resources"(C) is an action distinguishes it from being part of "computability theory"(B), so "imposing restrictions on the available resources" belongs to "computational complexity"(A)