code: func (c *cNode) renewed(gen *generation, ctrie *Ctrie) *cNode {
  	array := make([]branch, len(c.array))
  	for i, br := range c.array {
  		switch t := br.(type) {
  		case *iNode:
  			array[i] = t.copyToGen(gen, ctrie)
  		default:
  			array[i] = br
  		}
  	}
  	return &cNode{bmp: c.bmp, array: array, gen: gen}
  }
docs: // renewed returns a copy of this cNode with the I-nodes below it copied to the
  // given generation.