Translate each of these nested quantifications into an English statement that expresses a mathematical fact. The domain in each case consists of all real numbers.
a) ∃x∀y(xy = y)
b) ∀x∀y(((x < 0) ∧ (y < 0)) → (xy > 0))
c) ∃x∃y((x2 > y) ∧ (x < y))
d) ∀x∀y∃z(x + y = z)