It makes me wonder what should be studied first - whether the basics of axiomatic set theory or mathematical logic? Although I initially that logic should be studied first, set theory second, now something makes me think that it should be vice-versa. The reason for this shift is that - when studying logic - we use various concepts that are introduced in set theory - numbers (&mathematical induction), sequence (definition of proof*) etc. What do you think? *formal proof is usually defined as follows: "a formal proof in propositional logic is a finite sequence of statements ..."