Armin Janssen, who later called himself Antonio Robledo, studied piano with Carl Seemann at the Freiburg University of Music from 1948 to 1949. He shared a warm friendship and a kindred spirit with Bertold Hummel, which Armin Janssen later alluded to in a letter:

Zurich, 26 December 1994

Dear Bertold,
Just a quick note … warm regards and best wishes for the New Year.
Even though we have drifted apart over almost half a century and hardly know each other any more, might there still be something left somewhere of the common ground and formative experiences from our early days, that lovely time in Freiburg?

A thousand greetings to you both from the two of us. Yours, Armin

Armin Janssen played the piano part at the world premiere of the Sonatina for Trumpet and Piano, Op. 1a

Biography
Antonio Robledo (Theatre Encyclopaedia of Switzerland, 2005)