给定集合A和集合B，它们的交集和并集可以通过下面的运算实现，那么求A在B中的相对补集怎么操作啊
julia> A = ["a", "b", "c"]
3-element Array{String,1}:
"a"
"b"
"c"
julia> B = ["b", "c", "d"]
3-element Array{String,1}:
"b"
"c"
"d"
julia> A∩B
2-element Array{String,1}:
"b"
"c"
julia> A∪B
4-element Array{String,1}:
"a"
"b"
"c"
"d"
可以通过下面函数实现，我想问的是julia中有没有相应的操作符来操作啊
julia> filter(x->x∉A, B)
1-element Array{String,1}:
"d"