[1,1,2,3,1,2] -> [1,2,3].

[1,1,2,3,1,2] -> [3,1,2].

ElementEqual checks if two slices have the same elements, but not necessarily in the same order.

a == b only if a and b have the same elements in the same order.

a has v.

X > Y.

a & b , in the order of a.

merge all slices into one.

reverse the slice in place.

a - b , in the order of a.

a | b , in the order of a.