If you hit ; (semicolon) following the retrieval of a solution, the system will attempt to resatisfy your goal:
|?X = NIL
|?Y = (1 2);
|
|?X = (1)
|?Y = (2);
|
|?X = (1 2)
|?Y = NIL;
|
|NO.
|
|==>
When no more solutions remain, NO. is displayed and you are back at the top level.
KnowledgeWorks and Prolog User Guide (Macintosh version) - 26 Feb 2015