J'ai réalisé quelques objets 3D manipulables permettant de se représenter le cross-cap, à partir du "pliage" d'une topologie plane, et également de l'obstruction liée à sa représentation par un "recouvrement" sphérique. À toute fin utile... Le vendredi 25 septembre 2026 à 10:50:19 UTC+2, Jacques B. Siboni via Topologos <topologos@lutecium.org> a écrit : Dear friends and colleagues Our last workshop on September 12 is now available on YouTube, there is some delay to find it on Lutecium, it will be available probably soon. But you can have an access to it there: Topologies of the Object #2 the chapters we have been through are: 5. Geometry of the Projective Plane6. Standing on the Object a7. Navigate over the Projective Plane; R schema, I Schema8. Small encounter with the Cross Cap9. Crossing over the Phantasm (revisited) A third one will take place in October or maybe in November Your comments are welcome All the best Jacques -- You are receiving this message because you are subscribed to the "Topologos" mailing list, which now combines the former "lutecium-group" and "topologos-workshop" lists. Topologos mailing list -- topologos@lutecium.org To unsubscribe send an email to topologos-leave@lutecium.org