[seqfan] lattice paths

[Brendan McKay]

Consider walks in { (x,y) | x,y >= 0 } with steps of
size (1,2) and (1,-3), starting at (0,0).

Typical walk: (0,0), (1,2), (2,4), (3,1), (4,3), (5,0), (6,2).

This example has vertical step set {-3,2} but of course it 
could be any set of integers.

Where are such walks analysed? Surely there is a definitive
treatment somewhere, but the literature on lattice walks is so vast
that finding the right trees amongst all the wood is a bit of a
struggle.

Thanks,
Brendan.