If I recall correctly, Grothendieck was at the Seminaire Cartan prior to writing his Tohoku article, and the homological algebra there influenced his work. (I also recall a quote about Grothendieck loathing diagrams (or spectral sequences?) at the seminar.) But now I cannot find a reference for this fact. Any pointer to one would be appreciated.
(I know Grothendieck was at the Seminare 1948-1949 (50?), but today I started wondering if he was there any sooner time before 1955, which is why I ask.)