; .
The two "67" Algorithms in Equation 19 are somewhat different. The first one, applied to N-1 disks, is actually "67-Down" Algorithm. The second one, applied to N-2 disks, is actually "67-Up" Algorithm. The "67-Up" Algorithm is a "time-reversed" "67-Down" Algorithm (and vice-versa – see Appendix 1). Necessarily, the move-counting equations related to the "67" Algorithm (Equations 10 and 12) apply equally well to both algorithms.