Hermann Zapf retrofitted the mathematical principle on his typeface Melior after the fact. Melior was drawn without any mathematical exactness, it’s very calligraphic in its details. It was designed in the 1950s, and the superellipse became popular in architecture in the 1960s, so Zapf gladly made the connection to his typeface.John Savard said:Of course, the first thing I thought of when I saw that you were doing a typeface based on a shape intermediate between a square and a circle was Melior, designed by Hermann Zapf using the superellipse of Piet Hein.