code: def subtract(self, jobShape):
          
          self.shape = Shape(self.shape.wallTime,
                             self.shape.memory - jobShape.memory,
                             self.shape.cores - jobShape.cores,
                             self.shape.disk - jobShape.disk,
                             self.shape.preemptable)
docs: Subtracts the resources necessary to run a jobShape from the reservation.