Free augmented LD-systems
Résumé
Define an augmented LD-system, or ALD-system, to be a set equipped with two binary operations, one satisfying the left self-distributivity law $x * (y * z) = (x * y) * (x * z)$ and the other satisfying the mixed laws $(x o y) * z = x * (y * z)$ and $x * (y o z) = (x * y) o (x * z)$. We solve the word problem of the ALD laws, and prove that every element in the parenthesized braid group $B_\bullet$ of [Bri1, Dhb, Dhe] generates a free ALD-system of rank 1, thus getting a concrete realization of the latter structure.