Enflo's example of a Banach space without the approximation property
Séminaire Équations aux dérivées partielles (Polytechnique) (1972-1973), Talk no. 8, 9 p.
@article{SEDP_1972-1973____A9_0,
     author = {Kwapien, S.},
     title = {Enflo's example of a Banach space without the approximation property},
     journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique)},
     publisher = {Ecole Polytechnique, Centre de Math\'ematiques},
     year = {1972-1973},
     note = {talk:8},
     zbl = {0263.46018},
     mrnumber = {407569},
     language = {en},
     url = {http://www.numdam.org/item/SEDP_1972-1973____A9_0}
}
Kwapien, S. Enflo's example of a Banach space without the approximation property. Séminaire Équations aux dérivées partielles (Polytechnique) (1972-1973), Talk no. 8, 9 p. http://www.numdam.org/item/SEDP_1972-1973____A9_0/

[1] P. Enflo: A counterexample to the approximation problem, to appear in Acta Math. | MR 402468 | Zbl 0267.46012

[2] A. Grothendieck: Produits tensoriels topologiques et espaces nucléaires, Mem. Amer. Math. Soc. 16 (1956). | Zbl 0123.30301

[3] A. Zygmund: Trigonometrical series.