A lattice polygon formed by a three-choice walk. The anisotropic perimeter and area generating function
 |
where 
is the number of polygons with 
horizonal bonds, 
vertical bonds, and area 
, 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 
has a logarithmic singularity and so is not algebraic, but is known to be D-finite
(Conway et al. 1997, Bousquet-Mélou 1999).
The anisotropic area and perimeter generating function 
satisfies an inversion relation of
the form
 |
(Bousquet-Mélou et al. 1999).
