code: func Merge(coll1, coll2 []string) []string {
  	m := map[string]struct{}{}
  	for _, v := range append(coll1, coll2...) {
  		m[v] = struct{}{}
  	}
  	r := make([]string, 0, len(m))
  	for k := range m {
  		r = append(r, k)
  	}
  	return r
  }
docs: // Merge performs a union of two string slices: the result is an unordered slice
  // that includes every item from either argument exactly once