Matches any of the patterns of the comma separated list between the braces. Generate a unique atom from base Base and unify it with Unique . Base should be an atom. Note that this is no warrant that the atom is unique in the system. Suspend execution Time seconds.
Time is either a floating point number or an integer.
Granularity is dependent on the system's timer granularity. A negative time causes the timer to return immediately. On most non-realtime operating systems we can only ensure execution is suspended for at least Time seconds.