sub in {
  my($inQuestion)= shift;
  foreach (@_) {
    return 1 if $_ eq $inQuestion;
  }
  return false;
}

##</code><code>##

in($question, "a", "b", "c");

##</code><code>##

if ($day =~ /^(?:Mo|Tu|We|Th|Fr|Sa|Su)$/) ...

##</code><code>##

if (defined $mnth= $monthNum{$month}) ...