The Electronic Journal of Combinatorics

v16i1r72 — Comment by the second author, Dec 16, 2009.

Thomas Prellberg has kindly pointed out that yet another proof of our Theorem 4 can be found in:

A. J. Guttman and T. Prellberg,
Staircase polygons, elliptic integrals, Heun functions, and lattice Green functions,
Physical Review E 47 (4) (1993), R2233-R2236.