Propergate Up Tree

• u₁ is now propergated up the tree to the next function

• Its other argument is determined
• N_jk is multiplied by it to yield M₂.

  E.g. $M_2 = u_{x} N_{-,\mbox{left}}$

  $u_{x-y/3}= u_{y/3}M_2 = u_{y/3}u_{x} N_{-,\mbox{left}}$