In 1975 A. Cordoba and R. Fefferma gave a combinatorial-geometric proof of the boundedness results of B. Jessen, J. Marcinkiewicz and A. Zygmund for the strong maximal function (1935). In this expository seminar, we go through the details of their rather coincise proof. The original article is Cordoba, A.; Fefferman, R. A geometric proof of the strong maximal theorem, Ann. of Math. 102 (1975), no. 1, 95–100.