Consider a particle that can move in a plane only in a rectangular arrangement $($a mesh

square of length l$)$ infinite, the probabilities are p$1,$ p$2,$ p$3$ and p$4$ as seen in Figure $3\mathrm{.}1.$

Let us discuss the homogeneous case, in which the probabilities are the same, i$.$e$.,$ pi $=1/4$ for i $=1,2,3,4.$

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