Write a program which takes two arrays of positive integers as input. One of them (your choice which) will have one item missing compared to the other. Your program must figure out what is missing.
You can choose which array has one missing: You can take ordinary then missing or vice versa.
Arrays may contain duplicates.
[1,2,3], [1,3] => 2 [3,3,3,3,3], [3,3,3,3] => 3 [4,6,1,6,3,5,2], [3,6,2,5,4,6] => 1 [9,9,10,645,134,23,65,23,45,12,43], [43,134,23,65,12,9,10,645,45,9] => 23
This is code-golf, shortest bytes wins!