$a = 5;
$b = 5;
$c = 5;
if ((($a == $b ) + ($a -1)) == $c) { print "yes!!!\n"; }

##</code><code>##

$a = 6;
$b = 5;
$c = 5;
if ((($a == $b ) + ($a -1)) == $c) { print "yes!!!\n"; }

##</code><code>##

# given three equal variables
if (($a == $b ) == ($b == $c)) { print "yes!!!\n"; }

##</code><code>##

$a = 6;
$b = 4;
$c = 5;
if (($a == $b ) == ($b == $c)) { print "yes!!!\n"; }