code: def check_collision_state( cls, collision_state, history_id_key, history_id, block_id, checked_ops, affected_opcodes ):
          
  
          # seen before in this block?
          if collision_state.has_key( block_id ):
              if collision_state[block_id].has_key(history_id_key):
                  if history_id in collision_state[block_id][history_id_key]:
                      rc = True
  
                  else:
                      collision_state[block_id][history_id_key].append( history_id )
                      rc = False
  
              else:
                  collision_state[block_id][history_id_key] = [history_id]
                  rc = False
  
          else:
              collision_state[block_id] = { history_id_key: [history_id] }
              rc = False
  
          if not rc:
              # no collision 
              return rc
  
          # find and mark collided operations 
          for prev_op in checked_ops:
  
              prev_opcode = op_get_opcode_name( prev_op['op'] )
              if prev_opcode not in affected_opcodes:
                  # not affected
                  continue 
  
              if history_id_key not in prev_op:
                  # won't match
                  continue
  
              if prev_op[history_id_key] == history_id:
                  # collision 
                  cls.nameop_set_collided( prev_op, history_id_key, history_id )
  
          return True
docs: Given a history ID, see if it already exists
          at the given block ID (i.e. it's not expired),
          using the given collision state.
          Return True if so; False if not.
          If there is a collision, set the __collided__ field in each checked_ops that
          has a matching history_id value and has an opcode in affected_opcodes.