Polyhedral Version
The Crosscap.
It is one of the various manifestations of the projective plane. See
. This surface has two “cuspidal points”, or “umbrellas of
. See also the article for a better understanding. The psychoanalyst Jacques Lacan saw this as an image of the “fundamental fantasy” and placed “object a”, the “linguistic phallus”, at the central cuspidal point. See “J.P.Petit in Jacques Lacan”.
With a bit of dexterity, enter inside the Crosscap to observe from this viewpoint the central cuspidal point and note that it is identical to the other one.