<div class="notebook"> <div class="nb-cell program" name="p1"> reduce3(_, [], Default, Default). reduce3(_, [A], _, A). reduce3(P3, [A,B|T], _, D):- call(P3, A, B, C), reduce3(P3, [C|T], _, D). strings_concate(Strings, String):- reduce3(string_concat, Strings, "", String). </div> <div class="nb-cell query" name="q1"> reduce3(string_concat, ["123", "456", "789"], "", R). </div> <div class="nb-cell query" name="q2"> reduce3(string_concat, ["123", "456"], "", R). </div> <div class="nb-cell query" name="q3"> reduce3(string_concat, ["123"], "", R). </div> <div class="nb-cell query" name="q4"> reduce3(string_concat, [], "", R). </div> <div class="nb-cell query" name="q5"> strings_concate(["123", "456"], R). </div> </div>