Prologの技芸 2.3節の練習問題

サンプルデータベース

on(block1,block2).
on(block2,block3).
on(block3,block4).
on(block5,block6).
on(block6,block7).

(1)

above(Block1,Block2) :- on(Block1,Block2).
above(Block1,Block2) :-
 on(Block1,Block), above(Block,Block2).