recursion which we first return to the second column and try alternate positions for that queen before possibly having to return all the way back to the first column the next step is to return to the second column and pick up the queen we placed at position ( and remove the markers that were used to indicate the squares that queen was guarding we then place the queen at the next available square within the same column ( and mark the appropriate squares guarded from this positionas shown herex now we can return to the third column and try again this timewe place queen at position ( )but this results in no open squares in the fourth column we could try other squares in the same columnbut none are open thuswe must pick up the queen from the third column and again backtrack to try other combinations we return to the second column and pick up the queen we placed earlier at position ( so we can try other squares within this column but there are no more open squares in the second column to tryso we must back up even furtherreturning to the first column when returning to columnthe first step is always to pick up the queen previously placed in that column