(*bt-all*)
(* Modified version of bt0, delivers all solutions to nqueens *)

fun bt0 k m n p =
    if k>n
    then let val (pk,pm) = hd p
         in p:: bt0 pk (pm+1) n (tl p) end
    else if p=[] andalso m>n
         then []
         else if m>n
              then let val (pk,pm)=hd p            
                   in bt0 pk (pm+1) n (tl p) end  
                   else if check nq (k,m) p      
                        then bt0 (k+1) 1 n ((k,m)::p) 
                        else bt0 k (m+1) n p;