Gessel's walks are the planar walks that move within the positive quadrant
Z+2 by unit steps in any of the following directions: West,
North-East, East and South-West. In this paper, we find an explicit expression
for the trivariate generating function counting the Gessel's walks with k≥0 steps, which start at (0,0) and end at a given point (i,j)∈Z+2.Comment: 23 page