alias rps {
  var %r s,%p r,%s p,%% return
  if $0 = 2 && $count(rps,$1,$2) = 2 && $len($1 $+ $2) = 2 {
    if ($1 = $2) %% 0
    if ($1 = $(% $+ $2,2)) %% 2
    %% 1
  }
  %% -1
}