rem: err |= open_next_file ();
add: ok &= open_next_file ();
context: read_char (int *c){  int err = 0;  *c = EOF;  while (in_stream != NULL)	/* EOF.  */    {      *c = fgetc (in_stream);      if (*c != EOF)	break;      err |= check_and_close ();      err |= open_next_file ();    }  return err;}