clpStatistic's values; otherwise fails. Example:
?- clpStatistics, X::real, {X**4-4*X**3+4*X**2-4*X+3==0}, clpStatistics(Ss).
Ss = [userTime(0.023398999999999504), gcTime(0.001), globalStack(19216/131040), trailStack(1296/133096), localStack(2184/118648), inferences(82961), narrowingOps(2245), narrowingFails(0), node_count(9), max_iterations(2245/3000)],
X::real(-1.509169756145379, 4.18727500493995).