[Izkata]

I'm guessing because their understanding is still wrong:

  3> log10 5 + 5 + log10 5 + 5    ;; i.e. (log10 5 + 5) + (log10 5 + 5)
  2.0

In Rebol this would be equivalent to (log10 (5 + (5 + (log10 (5 + 5)))))