$IP = $ENV{'REMOTE_ADDR'};  ## Yes, there are caveats here...
$lastpost = $lastpost{$IP}; ## Stored in a database
## ($lastpost is a hashref)
if (
  $user           eq $lastpost->{"USER"}     and
  $Q::lastnode_id == $lastpost->{"LASTNODE"} and 
  $Q::node        eq $lastpost->{"NODE"}     and 
  !$Q::PostAnywayCheckbox
) {
  &DoubledPost;
}