Geodesic
The simplest example of a completely regular, non-normal space
Problemy analiza, no. 4 (1997), pp. 97-98.

Voir la notice de l'article provenant de la source Math-Net.Ru

Still another example of a completely regular nonnormal space is given. This one is marked by brevity, clarity and graphic representation, which may be of some interest to those who teach general topology to students. 
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K. V. Matyushichev. The simplest example of a completely regular, non-normal space. Problemy analiza, no. 4 (1997), pp. 97-98. http://geodesic.mathdoc.fr/item/PA_1997_4_a6/