@article{BSMA_1882_2_6_1_111_0, author = {Weierstrass, C.}, title = {Recherches sur les fonctions $2r$ fois p\'eriodiques de $r$ variables. {(Lettres} de {M.} {C.} {Weierstrass} \`a {M.} {C.-W.} {Borchardt)}}, journal = {Bulletin des Sciences Math\'ematiques et Astronomiques}, pages = {111--120}, publisher = {Gauthier-Villars}, volume = {2e s{\'e}rie, 6}, number = {1}, year = {1882}, language = {fr}, url = {http://archive.numdam.org/item/BSMA_1882_2_6_1_111_0/} }