Non Ecludiean geometry
Let’s walk (and dogsled, and swim) from the North Pole along the Greenwich meridian (0 deg. longitude) through England and down to the Equator. Here make a right turn. That’s a 90 degree angle. Go until you hit San Salvador Island, west of Ecuador, located on the Equator at the 90th meridian (+90 degrees) . … Leer más »