PHP递归函数错误？

function factorial($n) {
    if ($n <= 1) {
        return 1;
    }
    return $n * factorial($n - 1);
}

function factorial($n, $acc = 1) {
    if ($n <= 1) {
        return $acc;
    }
    return factorial($n - 1, $n * $acc);
}

function infiniteRecursion() {
    return infiniteRecursion();
}

function factorial($n) {
    if ($n <= 1) {
        return 1;
    }
    return $n * factorial($n - 1);
}

function fibonacci($n, &$memo = []) {
    if (isset($memo[$n])) {
        return $memo[$n];
    }
    if ($n <= 1) {
        return $n;
    }
    $memo[$n] = fibonacci($n - 1, $memo) + fibonacci($n - 2, $memo);
    return $memo[$n];
}