Primitive Two-Dimensional Words and Iterated Pedal Triangles via Symbolic Coding
This work connects two previously unrelated areas—combinatorics on words and geometry—providing a novel theoretical link for researchers in both fields.
The authors establish a bijection between primitive two-dimensional words of dimension 2×n over a binary alphabet and triangles whose first similar pedal triangle is their nth pedal triangle, using a finite four-symbol coding of the sorted pedal map.
The notion of a two-dimensional word arises naturally in the study of combinatorics on words, while the iterative construction of pedal triangles results in a rich dynamical system in the study of geometry. At first, these two classes of objects seem to be unrelated. However, it is known that for all $n \geq 1$, the number of primitive two-dimensional words of dimension $2 \times n$ over a binary alphabet agrees with the number of triangles whose first similar pedal triangle is their $n$th pedal triangle. We construct a finite four-symbol coding of the sorted pedal map and use the resulting branch itineraries to give a bijection between these two classes.