<?php

function afisare_combinari($a, $len)
{
    if ($len > count($a))
        return 'error';
    $out = array();
    if ($len == 1) {
        foreach ($a as $v)
            $out[] = array($v);
        return $out;
    }

    $len--;

    while (count($a) > $len) {
        $b = array_shift($a);
        $c = afisare_combinari($a, $len);

        foreach ($c as $v) {
            array_unshift($v, $b);
            $out[] = $v;
        }
    }
    return $out;
}

$values = array("A", "B", "C", "D");

//var_dump(afisare_combinari($values, 2));

/* * **************************** */

$base = array("A", "B");

var_dump(array_filter(afisare_combinari($values, 2), function($subArr) use ($base) {
                    return in_array($subArr[0], $base);
                }
        ));