Nondeterministically instantiates a domain variable to its domain values. The order of enumeration is in increasing term order (i.e. alphabetic for atoms).
?- X &:: [mo, tu, we, th, fr, sa, su], indomain(X). X = fr Yes (0.00s cpu, solution 1, maybe more) X = mo Yes (0.05s cpu, solution 2, maybe more) X = sa Yes (0.06s cpu, solution 3, maybe more) X = su Yes (0.06s cpu, solution 4, maybe more) X = th Yes (0.06s cpu, solution 5, maybe more) X = tu Yes (0.07s cpu, solution 6, maybe more) X = we Yes (0.08s cpu, solution 7) ?- indomain(we). Yes (0.00s cpu)