With the most language, Goal is bound to the most specific generalization of all its solutions. If one of the solutions is not a variant of this answer, the goal is delayed until one of its variables is bound. Note that the Goal may have an infinity of solutions.
Using other languages, an approximation of this most specific generalization can be computed. With the ground language, infers/2 instantiates the Goal only if the solutions of Goal are all the same ground term. If not, the goal is delayed until one of its variables is bound. With the consistent language, infers/2 does not bind the Goal but only checks if Goal has at least one solution. In this case, the goal is delayed until one of its variables is bound.
Success: [eclipse]: member(X, [f(1), f(2)]) infers most. X = f(_g1075[1, 2]) yes. [eclipse]: [user]. and(0, _, 0). and(_, 0, 0). and(1, 1, 1). user compiled traceable 528 bytes in 0.00 seconds yes. [eclipse]: and(0, X, Y). X = X Y = 0 More? (;) % Prolog: two solutions X = 0 Y = 0 yes. [eclipse]: and(0, X, Y) infers most. X = X Y = 0 yes. % Prolog + infers: one solution [eclipse]: [user]. greater_than(succ(X), X). greater_than(succ(X), Y) :- greater_than(X, Y). user compiled traceable 268 bytes in 0.00 seconds yes. [eclipse]: greater_than(X, zero). X = succ(zero) More? (;) % Prolog: infinity of solutions ... [eclipse]: greater_than(X, zero) infers most. X = succ(_g1073) Delayed goals: infers(greater_than(succ(_g1073), zero), most, eclipse) yes. Fail: [eclipse]: member(1, [2, 3]) infers consistent. no (more) solution. Error: Goal infers most. % Error 4 true infers true. % Error 6