php怎么判断一个数组中的元素是否完全属于另一个数组

<?php
header("Content-type:text/html;charset=utf-8");
$arr1=array("a"=>"red","b"=>"green","c"=>"blue","d"=>"yellow");
$arr2=array("a"=>"red","b"=>"green","c"=>"blue");
var_dump($arr1);
var_dump($arr2);

//利用array_intersect_assoc()函数比较数组a和数组b，取交集
echo "交集数组：";
$intersect=array_intersect_assoc($arr1,$arr2);
var_dump($intersect);

//利用array_diff_assoc()函数比较数组a和交集数组，取差集
echo "差集数组：";
$diff=array_diff_assoc($intersect,$arr2);

//利用“==”运算符判断差集数组是否为空
var_dump($diff);
if($diff==[]){
    echo '$arr2完全属于$arr1';
}else{
    echo '$arr2不完全属于$arr1';
}
?>