code: def _add_boundaries(self, interval):
          
          begin = interval.begin
          end = interval.end
          if begin in self.boundary_table:
              self.boundary_table[begin] += 1
          else:
              self.boundary_table[begin] = 1
  
          if end in self.boundary_table:
              self.boundary_table[end] += 1
          else:
              self.boundary_table[end] = 1
docs: Records the boundaries of the interval in the boundary table.