rand(0) returns a pseudo random number in the interval [0:1] generated from the current value of two internal 32-bit seeds. rand(-1) resets both seeds to a standard value. rand(x) for integer 0 < x < 2^31-1 sets both internal seeds to x. rand({x,y}) for integer 0 < x,y < 2^31-1 sets seed1 to x and seed2 to y.