A lattice polygon formed by a three-choice walk. The anisotropic perimeter and area generating function G(x, y, q) = sum_(m>=1) sum_(n>=1) sum_(a>=a) C(m, n, a) x^m y^n q^a, where C(m, n, a) is the number of polygons with 2m horizonal bonds, 2n vertical bonds, and area a, is not yet known in closed form, but it can be evaluated in polynomial time (Conway et al. 1997, Bousquet-Mélou 1999). The perimeter-generating function G(x, x, 1) has a logarithmic singularity and so is not algebraic, but is known to be D-finite (Conway et al. 1997, Bousquet-Mélou 1999).