# Lesson I Before ink, there is only the hand and the sheet before it. Nothing more is needed. Practice is lost when the hand reaches past what is present. ## Try ```prolog % ?- program([dup, swap, over]). % true. % ?- program([dup, made_up]). % false. ``` ## Learn ```prolog % A program is made from known core words. word(dup). word(drop). word(swap). word(over). % A program is a list of words. Validation walks that list % recursively. run([]). run([Word|Words]) :- word(Word), program(Words). ```