inlist(1,L,[1|L]).
inlist(X,L1,L2):-
X>1,
Y is X-1,
inlist(Y,[X|L1],L2).

queens(N,Solutions):-
inlist(N,[],L),
solve([],Solutons,L,L).

solve(Input,Output,[Row|R],Columns):-
choose(Col,Columns,C),
Up is Row+Col,
Down is Row-Col,
safe(Up,Down,Input),
solve([square(Col,Up,Down)|Input],Output,R,C).
solve(L,L,[],[]).

choose(X,[X|Y],Y).
choose(X,[H|T1],[H|T2]):-
choose(X,T1,T2).

safe(U1,D1,[square(_,U,D)|Rest]):-
U1\=U,D1\=D,
safe(U1,D1,Rest).
safe(_,_,[]).

n_queens:-
write("The size of the chessboar N="),
read(N),
queens(N,Solutions),
print_board(N,Solutions),
fail.

print_board(N,[square(X,_,_)|L]):-
nl,
Y is X-1,
write_dots(Y),
write(Q),
W is N-X,
write_dots(W),
print_board(N,L).

write_dots(X):-
X>0,
write("."),
Y is X-1,
write_dots(Y).

write_dots(0).


n_queens.
The size of the chessboar N=2
THE$126
Syntax error in parser
No solutions
Reconsulted from: C:\Documents and Settings\Administrator\My Documents\Visual Prolog 7.0 Examples\pie\EXE\FILE6.PRO
n_queens.
The size of the chessboar N=Trace is On
3
Trace: >> CALL:   queens(3,SOLUTIONS$127)
Trace: >> CALL:   inlist(3,[],L$128)
Trace: >> CALL:   3 > 1
Trace: >> RETURN: 3 > 1
Trace: >> CALL:   Y$129 is 3 - 1
Trace: >> RETURN: 2 is 3 - 1
Trace: >> CALL:   inlist(2,[3|[]],L$128)
Trace: >> CALL:   2 > 1
Trace: >> RETURN: 2 > 1
Trace: >> CALL:   Y$130 is 2 - 1
Trace: >> RETURN: 1 is 2 - 1
Trace: >> CALL:   inlist(1,[2|[3|[]]],L$128)
Trace: >> RETURN: inlist(1,[2|[3|[]]],[1|[2|[3|[]]]])
Trace: >> RETURN: inlist(2,[3|[]],[1|[2|[3|[]]]])
Trace: >> RETURN: inlist(3,[],[1|[2|[3|[]]]])
Trace: >> CALL:   solve([],SOLUTONS$131,[1|[2|[3|[]]]],[1|[2|[3|[]]]])
Trace: >> CALL:   choose(COL$132,[1|[2|[3|[]]]],C$133)
Trace: >> RETURN: choose(1,[1|[2|[3|[]]]],[2|[3|[]]])
Trace: >> CALL:   UP$134 is 1 + 1
Trace: >> RETURN: 2 is 1 + 1
Trace: >> CALL:   DOWN$135 is 1 - 1
Trace: >> RETURN: 0 is 1 - 1
Trace: >> CALL:   safe(2,0,[])
Trace: >> RETURN: safe(2,0,[])
Trace: >> CALL:   solve([square(1,2,0)|[]],SOLUTONS$131,[2|[3|[]]],[2|[3|[]]])
Trace: >> CALL:   choose(COL$136,[2|[3|[]]],C$137)
Trace: >> RETURN: choose(2,[2|[3|[]]],[3|[]])
Trace: >> CALL:   UP$138 is 2 + 2
Trace: >> RETURN: 4 is 2 + 2
Trace: >> CALL:   DOWN$139 is 2 - 2
Trace: >> RETURN: 0 is 2 - 2
Trace: >> CALL:   safe(4,0,[square(1,2,0)|[]])
Trace: >> CALL:   4 \= 2
Trace: >> RETURN: 4 \= 2
Trace: >> CALL:   0 \= 0
Trace: >> FAIL:   0 \= 0
Trace: >> REDO:   4 \= 2
Trace: >> FAIL:   4 \= 2
Trace: >> FAIL:   safe(4,0,[square(1,2,0)|[]])
Trace: >> REDO:   0 is 2 - 2
Trace: >> FAIL:   DOWN$139 is 2 - 2
Trace: >> REDO:   4 is 2 + 2
Trace: >> FAIL:   UP$138 is 2 + 2
Trace: >> REDO:   choose(2,[2|[3|[]]],[3|[]])
Trace: >> CALL:   choose(COL$136,[3|[]],T2$140)
Trace: >> RETURN: choose(3,[3|[]],[])
Trace: >> RETURN: choose(3,[2|[3|[]]],[2|[]])
Trace: >> CALL:   UP$138 is 2 + 3
Trace: >> RETURN: 5 is 2 + 3
Trace: >> CALL:   DOWN$139 is 2 - 3
Trace: >> RETURN: -1 is 2 - 3
Trace: >> CALL:   safe(5,-1,[square(1,2,0)|[]])
Trace: >> CALL:   5 \= 2
Trace: >> RETURN: 5 \= 2
Trace: >> CALL:   -1 \= 0
Trace: >> RETURN: -1 \= 0
Trace: >> CALL:   safe(5,-1,[])
Trace: >> RETURN: safe(5,-1,[])
Trace: >> RETURN: safe(5,-1,[square(1,2,0)|[]])
Trace: >> CALL:   solve([square(3,5,-1)|[square(1,2,0)|[]]],SOLUTONS$131,[3|[]],[2|[]])
Trace: >> CALL:   choose(COL$141,[2|[]],C$142)
Trace: >> RETURN: choose(2,[2|[]],[])
Trace: >> CALL:   UP$143 is 3 + 2
Trace: >> RETURN: 5 is 3 + 2
Trace: >> CALL:   DOWN$144 is 3 - 2
Trace: >> RETURN: 1 is 3 - 2
Trace: >> CALL:   safe(5,1,[square(3,5,-1)|[square(1,2,0)|[]]])
Trace: >> CALL:   5 \= 5
Trace: >> FAIL:   5 \= 5
Trace: >> FAIL:   safe(5,1,[square(3,5,-1)|[square(1,2,0)|[]]])
Trace: >> REDO:   1 is 3 - 2
Trace: >> FAIL:   DOWN$144 is 3 - 2
Trace: >> REDO:   5 is 3 + 2
Trace: >> FAIL:   UP$143 is 3 + 2
Trace: >> REDO:   choose(2,[2|[]],[])
Trace: >> CALL:   choose(COL$141,[],T2$145)
Trace: >> FAIL:   choose(COL$141,[],T2$145)
Trace: >> FAIL:   choose(COL$141,[2|[]],C$142)
Trace: >> FAIL:   solve([square(3,5,-1)|[square(1,2,0)|[]]],SOLUTONS$131,[3|[]],[2|[]])
Trace: >> REDO:   safe(5,-1,[square(1,2,0)|[]])
Trace: >> REDO:   safe(5,-1,[])
Trace: >> FAIL:   safe(5,-1,[])
Trace: >> REDO:   -1 \= 0
Trace: >> FAIL:   -1 \= 0
Trace: >> REDO:   5 \= 2
Trace: >> FAIL:   5 \= 2
Trace: >> FAIL:   safe(5,-1,[square(1,2,0)|[]])
Trace: >> REDO:   -1 is 2 - 3
Trace: >> FAIL:   DOWN$139 is 2 - 3
Trace: >> REDO:   5 is 2 + 3
Trace: >> FAIL:   UP$138 is 2 + 3
Trace: >> REDO:   choose(3,[2|[3|[]]],[2|[]])
Trace: >> REDO:   choose(3,[3|[]],[])
Trace: >> CALL:   choose(COL$136,[],T2$146)
Trace: >> FAIL:   choose(COL$136,[],T2$146)
Trace: >> FAIL:   choose(COL$136,[3|[]],T2$140)
Trace: >> FAIL:   choose(COL$136,[2|[3|[]]],C$137)
Trace: >> FAIL:   solve([square(1,2,0)|[]],SOLUTONS$131,[2|[3|[]]],[2|[3|[]]])
Trace: >> REDO:   safe(2,0,[])
Trace: >> FAIL:   safe(2,0,[])
Trace: >> REDO:   0 is 1 - 1
Trace: >> FAIL:   DOWN$135 is 1 - 1
Trace: >> REDO:   2 is 1 + 1
Trace: >> FAIL:   UP$134 is 1 + 1
Trace: >> REDO:   choose(1,[1|[2|[3|[]]]],[2|[3|[]]])
Trace: >> CALL:   choose(COL$132,[2|[3|[]]],T2$147)
Trace: >> RETURN: choose(2,[2|[3|[]]],[3|[]])
Trace: >> RETURN: choose(2,[1|[2|[3|[]]]],[1|[3|[]]])
Trace: >> CALL:   UP$134 is 1 + 2
Trace: >> RETURN: 3 is 1 + 2
Trace: >> CALL:   DOWN$135 is 1 - 2
Trace: >> RETURN: -1 is 1 - 2
Trace: >> CALL:   safe(3,-1,[])
Trace: >> RETURN: safe(3,-1,[])
Trace: >> CALL:   solve([square(2,3,-1)|[]],SOLUTONS$131,[2|[3|[]]],[1|[3|[]]])
Trace: >> CALL:   choose(COL$148,[1|[3|[]]],C$149)
Trace: >> RETURN: choose(1,[1|[3|[]]],[3|[]])
Trace: >> CALL:   UP$150 is 2 + 1
Trace: >> RETURN: 3 is 2 + 1
Trace: >> CALL:   DOWN$151 is 2 - 1
Trace: >> RETURN: 1 is 2 - 1
Trace: >> CALL:   safe(3,1,[square(2,3,-1)|[]])
Trace: >> CALL:   3 \= 3
Trace: >> FAIL:   3 \= 3
Trace: >> FAIL:   safe(3,1,[square(2,3,-1)|[]])
Trace: >> REDO:   1 is 2 - 1
Trace: >> FAIL:   DOWN$151 is 2 - 1
Trace: >> REDO:   3 is 2 + 1
Trace: >> FAIL:   UP$150 is 2 + 1
Trace: >> REDO:   choose(1,[1|[3|[]]],[3|[]])
Trace: >> CALL:   choose(COL$148,[3|[]],T2$152)
Trace: >> RETURN: choose(3,[3|[]],[])
Trace: >> RETURN: choose(3,[1|[3|[]]],[1|[]])
Trace: >> CALL:   UP$150 is 2 + 3
Trace: >> RETURN: 5 is 2 + 3
Trace: >> CALL:   DOWN$151 is 2 - 3
Trace: >> RETURN: -1 is 2 - 3
Trace: >> CALL:   safe(5,-1,[square(2,3,-1)|[]])
Trace: >> CALL:   5 \= 3
Trace: >> RETURN: 5 \= 3
Trace: >> CALL:   -1 \= -1
Trace: >> FAIL:   -1 \= -1
Trace: >> REDO:   5 \= 3
Trace: >> FAIL:   5 \= 3
Trace: >> FAIL:   safe(5,-1,[square(2,3,-1)|[]])
Trace: >> REDO:   -1 is 2 - 3
Trace: >> FAIL:   DOWN$151 is 2 - 3
Trace: >> REDO:   5 is 2 + 3
Trace: >> FAIL:   UP$150 is 2 + 3
Trace: >> REDO:   choose(3,[1|[3|[]]],[1|[]])
Trace: >> REDO:   choose(3,[3|[]],[])
Trace: >> CALL:   choose(COL$148,[],T2$153)
Trace: >> FAIL:   choose(COL$148,[],T2$153)
Trace: >> FAIL:   choose(COL$148,[3|[]],T2$152)
Trace: >> FAIL:   choose(COL$148,[1|[3|[]]],C$149)
Trace: >> FAIL:   solve([square(2,3,-1)|[]],SOLUTONS$131,[2|[3|[]]],[1|[3|[]]])
Trace: >> REDO:   safe(3,-1,[])
Trace: >> FAIL:   safe(3,-1,[])
Trace: >> REDO:   -1 is 1 - 2
Trace: >> FAIL:   DOWN$135 is 1 - 2
Trace: >> REDO:   3 is 1 + 2
Trace: >> FAIL:   UP$134 is 1 + 2
Trace: >> REDO:   choose(2,[1|[2|[3|[]]]],[1|[3|[]]])
Trace: >> REDO:   choose(2,[2|[3|[]]],[3|[]])
Trace: >> CALL:   choose(COL$132,[3|[]],T2$154)
Trace: >> RETURN: choose(3,[3|[]],[])
Trace: >> RETURN: choose(3,[2|[3|[]]],[2|[]])
Trace: >> RETURN: choose(3,[1|[2|[3|[]]]],[1|[2|[]]])
Trace: >> CALL:   UP$134 is 1 + 3
Trace: >> RETURN: 4 is 1 + 3
Trace: >> CALL:   DOWN$135 is 1 - 3
Trace: >> RETURN: -2 is 1 - 3
Trace: >> CALL:   safe(4,-2,[])
Trace: >> RETURN: safe(4,-2,[])
Trace: >> CALL:   solve([square(3,4,-2)|[]],SOLUTONS$131,[2|[3|[]]],[1|[2|[]]])
Trace: >> CALL:   choose(COL$155,[1|[2|[]]],C$156)
Trace: >> RETURN: choose(1,[1|[2|[]]],[2|[]])
Trace: >> CALL:   UP$157 is 2 + 1
Trace: >> RETURN: 3 is 2 + 1
Trace: >> CALL:   DOWN$158 is 2 - 1
Trace: >> RETURN: 1 is 2 - 1
Trace: >> CALL:   safe(3,1,[square(3,4,-2)|[]])
Trace: >> CALL:   3 \= 4
Trace: >> RETURN: 3 \= 4
Trace: >> CALL:   1 \= -2
Trace: >> RETURN: 1 \= -2
Trace: >> CALL:   safe(3,1,[])
Trace: >> RETURN: safe(3,1,[])
Trace: >> RETURN: safe(3,1,[square(3,4,-2)|[]])
Trace: >> CALL:   solve([square(1,3,1)|[square(3,4,-2)|[]]],SOLUTONS$131,[3|[]],[2|[]])
Trace: >> CALL:   choose(COL$159,[2|[]],C$160)
Trace: >> RETURN: choose(2,[2|[]],[])
Trace: >> CALL:   UP$161 is 3 + 2
Trace: >> RETURN: 5 is 3 + 2
Trace: >> CALL:   DOWN$162 is 3 - 2
Trace: >> RETURN: 1 is 3 - 2
Trace: >> CALL:   safe(5,1,[square(1,3,1)|[square(3,4,-2)|[]]])
Trace: >> CALL:   5 \= 3
Trace: >> RETURN: 5 \= 3
Trace: >> CALL:   1 \= 1
Trace: >> FAIL:   1 \= 1
Trace: >> REDO:   5 \= 3
Trace: >> FAIL:   5 \= 3
Trace: >> FAIL:   safe(5,1,[square(1,3,1)|[square(3,4,-2)|[]]])
Trace: >> REDO:   1 is 3 - 2
Trace: >> FAIL:   DOWN$162 is 3 - 2
Trace: >> REDO:   5 is 3 + 2
Trace: >> FAIL:   UP$161 is 3 + 2
Trace: >> REDO:   choose(2,[2|[]],[])
Trace: >> CALL:   choose(COL$159,[],T2$163)
Trace: >> FAIL:   choose(COL$159,[],T2$163)
Trace: >> FAIL:   choose(COL$159,[2|[]],C$160)
Trace: >> FAIL:   solve([square(1,3,1)|[square(3,4,-2)|[]]],SOLUTONS$131,[3|[]],[2|[]])
Trace: >> REDO:   safe(3,1,[square(3,4,-2)|[]])
Trace: >> REDO:   safe(3,1,[])
Trace: >> FAIL:   safe(3,1,[])
Trace: >> REDO:   1 \= -2
Trace: >> FAIL:   1 \= -2
Trace: >> REDO:   3 \= 4
Trace: >> FAIL:   3 \= 4
Trace: >> FAIL:   safe(3,1,[square(3,4,-2)|[]])
Trace: >> REDO:   1 is 2 - 1
Trace: >> FAIL:   DOWN$158 is 2 - 1
Trace: >> REDO:   3 is 2 + 1
Trace: >> FAIL:   UP$157 is 2 + 1
Trace: >> REDO:   choose(1,[1|[2|[]]],[2|[]])
Trace: >> CALL:   choose(COL$155,[2|[]],T2$164)
Trace: >> RETURN: choose(2,[2|[]],[])
Trace: >> RETURN: choose(2,[1|[2|[]]],[1|[]])
Trace: >> CALL:   UP$157 is 2 + 2
Trace: >> RETURN: 4 is 2 + 2
Trace: >> CALL:   DOWN$158 is 2 - 2
Trace: >> RETURN: 0 is 2 - 2
Trace: >> CALL:   safe(4,0,[square(3,4,-2)|[]])
Trace: >> CALL:   4 \= 4
Trace: >> FAIL:   4 \= 4
Trace: >> FAIL:   safe(4,0,[square(3,4,-2)|[]])
Trace: >> REDO:   0 is 2 - 2
Trace: >> FAIL:   DOWN$158 is 2 - 2
Trace: >> REDO:   4 is 2 + 2
Trace: >> FAIL:   UP$157 is 2 + 2
Trace: >> REDO:   choose(2,[1|[2|[]]],[1|[]])
Trace: >> REDO:   choose(2,[2|[]],[])
Trace: >> CALL:   choose(COL$155,[],T2$165)
Trace: >> FAIL:   choose(COL$155,[],T2$165)
Trace: >> FAIL:   choose(COL$155,[2|[]],T2$164)
Trace: >> FAIL:   choose(COL$155,[1|[2|[]]],C$156)
Trace: >> FAIL:   solve([square(3,4,-2)|[]],SOLUTONS$131,[2|[3|[]]],[1|[2|[]]])
Trace: >> REDO:   safe(4,-2,[])
Trace: >> FAIL:   safe(4,-2,[])
Trace: >> REDO:   -2 is 1 - 3
Trace: >> FAIL:   DOWN$135 is 1 - 3
Trace: >> REDO:   4 is 1 + 3
Trace: >> FAIL:   UP$134 is 1 + 3
Trace: >> REDO:   choose(3,[1|[2|[3|[]]]],[1|[2|[]]])
Trace: >> REDO:   choose(3,[2|[3|[]]],[2|[]])
Trace: >> REDO:   choose(3,[3|[]],[])
Trace: >> CALL:   choose(COL$132,[],T2$166)
Trace: >> FAIL:   choose(COL$132,[],T2$166)
Trace: >> FAIL:   choose(COL$132,[3|[]],T2$154)
Trace: >> FAIL:   choose(COL$132,[2|[3|[]]],T2$147)
Trace: >> FAIL:   choose(COL$132,[1|[2|[3|[]]]],C$133)
Trace: >> FAIL:   solve([],SOLUTONS$131,[1|[2|[3|[]]]],[1|[2|[3|[]]]])
Trace: >> REDO:   inlist(3,[],[1|[2|[3|[]]]])
Trace: >> REDO:   inlist(2,[3|[]],[1|[2|[3|[]]]])
Trace: >> REDO:   inlist(1,[2|[3|[]]],[1|[2|[3|[]]]])
Trace: >> CALL:   1 > 1
Trace: >> FAIL:   1 > 1
Trace: >> FAIL:   inlist(1,[2|[3|[]]],L$128)
Trace: >> REDO:   1 is 2 - 1
Trace: >> FAIL:   Y$130 is 2 - 1
Trace: >> REDO:   2 > 1
Trace: >> FAIL:   2 > 1
Trace: >> FAIL:   inlist(2,[3|[]],L$128)
Trace: >> REDO:   2 is 3 - 1
Trace: >> FAIL:   Y$129 is 3 - 1
Trace: >> REDO:   3 > 1
Trace: >> FAIL:   3 > 1
Trace: >> FAIL:   inlist(3,[],L$128)
Trace: >> FAIL:   queens(3,SOLUTIONS$

看不懂