A famous congruence equation question is the solvability of x y = c
(mod q) with x, y in intervals of length q^{1/2 + epsilon}. In this
talk, we will discuss its history and recent developments. We will show
that it is solvable for almost all pairs of intervals on x and y. Then,
out of the blue, it leads to a new attack on the problem through
'higher moments'.