sub prototyped($_;$)
{
  # Here $_[0] is a compulsory argument
  # $_[1] defaults to $_
  # $_[2] may not even exist
}

sub unprototyped
{
  push @_, $_ if @_ < 2;
  # Here $_[0] is a compulsory argument
  # $_[1] defaults to $_
  # $_[2] may not even exist
}