A letter

A letter on a postcard; no stamp, a fragment of a postal seal remains, label R - ie registered letter: Warschau C1 [below:] 307; seals with the so-called GAPA. There is also a number visible - stamped - next to the addressee's name (postal number, posting number?) 926070. The letter is from Warsaw to Artur Włodawer from Wiktor Włodawer, his younger brother, with the notes from: Szmul Ber (father), Lilka (sister), Lutek (?) and Bronka (?) (persons unknown), Natalia (Nachy) Blüth, Arthur Włodawer's older sister (with the son's name, Oleś, added). The sender's data was entered as: Joels Hercenbe [...] | Szpitalna 50 ap. 27 | Warschau .