Visualisation of the walk of string "abac" with forbidden points.

For simplicity, two letter repetitions are not included.

In case of abelian three letter {a,b,c} problem, where two letter "xx" and three letter "xxx" repetitions are allowed (and only them), the red points need to be avoided by all paths.

In case of abelian four letter {a,b,c,d} problem, the red points need to be avoided by consecutive paths of equal length.

In case of ordinary squares, the red points need to be avoided by consecutive paths of equal shape.