The same procedure works in reverse when encoding the direction attribute (Figure ). 2-butene having the syn conformation is modeled using a diagram whose left-and right-hand sides point downward and upward, respectively. The parent atom, a primary carbon, is identified. It is bonded to one neighbor through a PPB. To match the diagram, a direction of Down is assigned. The child atom is attached to its own child through a double bond. Finally, the grandchild is attached to its own child through a PPB whose direction is consistent with the diagram. A direction of Up is therefore assigned.