code: def reset(self):
          
          # Store positionned pieces on the board.
          self.pieces = set()
  
          # Squares on the board already occupied by a piece.
          self.occupancy = self.new_vector()
  
          # Territory susceptible to attacke, i.e. squares reachable by at least
          # a piece.
          self.exposed_territory = self.new_vector()
docs: Empty board, remove all pieces and reset internal states.