use Acme::Tools;
if (between($frequency, 10, 15) {print "Yes"}

##</code><code>##

if ($frequency == 10 .. 15) {print "Yes"}

##</code><code>##

if ( ($frequency == 10) .. 15 ) {print "Yes"}

##</code><code>##

my $frequency = 10;
if ($frequency == 10 .. 15) {print "Yes"}