  Consider a single walker on the slit plane, that is, the square grid Z^2
without its negative x-axis, who starts at the origin and takes his steps from
a given set S. Mireille Bousquet-Melou conjectured that -- excluding
pathological cases -- the generating function counting the number of possible
walks is algebraic if and only if the walker cannot cross the negative x-axis
without touching it. In this paper we prove a special case of her conjecture.
