From the book "Martine, petit rat de l'opéra" by Marcel Marlier & Gilbert Delahaye; or, as I knew it, "Anita no ballet". I remember propping this up on a music stand and doing the positions in my bedroom.
Strengthen your arch Sets: image is one set. Drill: as smoothly as possible moving through flex, Demi, point, and flex/curl. Then drill in reverse starting at image Tips: Keep legs active so that heals lift off the ground the entire time and sit up tall.