POSTKARTE Gabriel, Gábor Raimund Author: Gabriel, Gábor Raimund Recipient: Haeckel, Ernst Dating: 12.04.1911
TELEGRAMM Gabriel, Gábor Raimund Author: Gabriel, Gábor Raimund Recipient: Haeckel, Ernst Dating: 17.05.1911
BRIEF [O.A.] Gabriel, Gábor Raimund Author: Gabriel, Gábor Raimund Recipient: Haeckel, Ernst Dating: ??.??.1911