Set Theory Union of arrays in PHP

Question

There are 3 operations with sets in mathematics: intersection, difference and union (unification). In PHP we can do this operations with arrays:

• intersection:

Answer 1

The + operator:

$x[0] = 4;
$x[1] = 1;

$y[0] = 9;
$y[2] = 5;

$u = $y + $x;

// Results in:
$u[0] === 9;
$u[1] === 1;
$u[2] === 5;

Note that $x + $y != $y + $x