On Doors Being Simultaneously Open and Shut

Perhaps one of Marcel Duchamp's most obscure pieces is his Door, 11 rue Larrey. This was a door that that Duchamp had a carpenter construct in 1927 in the corner of a room in Duchamp's apartment. Because of this location, the door closed one entrance when it opened the other, thereby contradicting the French proverb Il faut qu'une porte soit ouverte ou fermée ['A door must be either open or closed']. 

This reminds me of the fact that Duchamp once wrote in a letter to the French poet André Breton Pour moi il y a autre chose que oui, non et indifférent - C’est par example l’absence d’investigations de ce genre ['For me there is something other than yes, no, and indifferent - there is for example the absence of investigations of this kind.']

You can read more about Door, 11 rue Larrey here on www.toutfait.com.