Indecomposable prefix codes and prime trees

A skate guard and walker comprising an elongate shoe containing an elongate groove for receiving the blade of a skate and heel and toe posts at the ends of the shoe containing forwardly and rearwardly-inclined recesses for receiving the ends of the blade and supporting frame, the heel and toe posts being relatively movable longitudinally of the shoe and a bolt associated with the heel post for adjustably fixing the position of the heel post in relation to the toe post.