code: def unassign(self, var, assignment):
          "Remove var from assignment (if it is there) and track conflicts."
          if var in assignment:
              self.record_conflict(assignment, var, assignment[var], -1)
          CSP.unassign(self, var, assignmentf unassign(self, var, assignment):
          "Remove var from assignment (if it is there) and track conflicts."
          if var in assignment:
              self.record_conflict(assignment, var, assignment[var], -1)
          CSP.unassign(self, var, assignment)
docs: Remove var from assignment (if it is there) and track conflicts.