<?php
    $a + $b; // (Union) Union of variables $a and $b
    $a == $b; // (Equality) True if $a and $b have same key/value pairs 
    $a == $b; // (Identity) True if $a and $b have same key/value pairs, in the same order and same types
    $a != $b; // (Inequality) True if $a is not equal $b
    $a <> $b; // (Inequality) True if $a is not equal $b
    $a !== $b; // (Non-identity) True is $a is not identical to $b
?>