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

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

# as pointed out by Sidhekin
# given three different variables
if (($a == $b ) == ($b == $c)) { print "yes!!!\n"; }

# still prints 'yes!!!\n'.  Why?
# both sides evaluate to false or 0, 
# and 0 == 0 evaluates to true
[download]

Update: Thanks to Sidhekin for pointing out my misstep. It does work with 2 same and 1 different variable. ;0)

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

Amel is one dangerous monk {grin} ... observe:

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

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

Yeah, right, "given three equal variables". Given three different variables, however ...

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

++ for not saying you'd use this ;-)

Update:... and here I had finally convinced myself Amel had to be joking ... oh well ...
You're welcome to that ++ anyways — the joke is none the worse for being unintended ;)

The Sidhekin
print "Just another Perl ${\(trickster and hacker)},"