code: func (c *cNode) updated(pos uint32, br branch, gen *generation) *cNode {
  	array := make([]branch, len(c.array))
  	copy(array, c.array)
  	array[pos] = br
  	ncn := &cNode{bmp: c.bmp, array: array, gen: gen}
  	return ncn
  }
docs: // updated returns a copy of this cNode with the entry at the given index
  // updated.