code: func differenceArrayArray(a, b *Container) *Container {
  	statsHit("difference/ArrayArray")
  	output := NewContainerArray(nil)
  	aa, ab := a.array(), b.array()
  	na, nb := len(aa), len(ab)
  	for i, j := 0, 0; i < na; {
  		va := aa[i]
  		if j >= nb {
  			output.add(va)
  			i++
  			continue
  		}
  
  		vb := ab[j]
  		if va < vb {
  			output.add(va)
  			i++
  		} else if va > vb {
  			j++
  		} else {
  			i, j = i+1, j+1
  		}
  	}
  	return output
  }
docs: // differenceArrayArray computes the difference bween two arrays.