  Let $\alpha = (1+\sqrt{5})/2$ and define the lower and upper Wythoff
sequences by $a_i = \lfloor i \alpha \rfloor$, $b_i = \lfloor i \alpha^2
\rfloor$ for $i \geq 1$. In a recent interesting paper, Kawsumarng et al.
proved a number of results about numbers representable as sums of the form $a_i
+ a_j$, $b_i + b_j$, $a_i + b_j$, and so forth. In this paper I show how to
derive all of their results, using one simple idea and existing free software
called Walnut. The key idea is that for each of their sumsets, there is a
relatively small automaton accepting the Fibonacci representation of the
numbers represented. I also show how the automaton approach can easily prove
other results.
