old_contents: #!/usr/bin/env python
  import math
  
  from geometry_msgs.msg import Point
  
  
  class NegativeTimeException(Exception):
      pass
  
  class Trajectory:
      def __init__(self):
          self.position = Point()
  
      def get_position_at(self, t):
          if t < 0:
              raise NegativeTimeException()
  
new_contents: #!/usr/bin/env python
  import math
  from twisted.conch.insults.insults import Vector
  
  from geometry_msgs.msg import Point
  
  
  class NegativeTimeException(Exception):
      pass
  
  class Trajectory:
      def __init__(self):
          self.position = Point()
  
      def get_position_at(self, t):
          if t < 0:
              raise NegativeTimeException()
  
  def abs_vector(self):
      return (self.x * self.x + self.y * self.y) ** 0.5
  
  
  def sub_point(self, other):
      return Vector(self.x - other.x, self.y - other.y)
  
  
  Vector.__abs__ = abs_vector
  Point.__sub__ = sub_point
  
subject: Implement __abs__ and __sub__ dunder methods