1) This is a common misunderstanding. ONLY the positive value of 'Y' is indicated by this expression. This IS a function.

2) Your example is good for y^2 = x-1, but it should be noted that x-1 >= 0 (Since y^2 >=- 0), making x >= 1 a pretty good guess at the Domain.

3) Please post responses on the original thread.