https://www.youtube.com/watch?v=X2muBFPw9cM
M.
-- ' A nun once asked a penguin ' do you think the earth is flat ? ; the penguin replied :
Madam, it all depends , in Riemann geometries the earth can be perfectly flat! The nun thanked him , he tripped and fell forward : the poor animal had forgotten that he might be living in a Riemann geometry too!
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