このディレクトリの索引 % list_nth/4 append/3(member/2)の変形 list_nth(N,L0,[A|R],L) :- integer(N), N > 0, M is N - 1, length(L0,M), append(L0,[A|R],L). list_nth(N,L0,[A|R],L) :- integer(N), N < 0, N1 is N + 1, N2 is abs(N1), length(R,N2), append(L0,[A|R],L). list_nth(N,L0,[A|R],L) :- var(N), append(L0,[A|R],L), length(L0,N1), N is N + 1.