Abstract evaluation

  <n(incr(incr(new(C)))),{ C }> -[new]-> 
  <n(incr(incr(C))),{ C[n:=0] }> -[incr]-> 
  <n(incr(C)),{ C[n:=1] }> -[incr]-> 
  <n(C), { C[n:=2] }> -[n]->
  <2, { C[n:=2] }>