Mitchell hung a mirror on the wall in his house.

To make sure it was perfectly straight he measured exactly 40 centimeters from each of two points along the left edge of the mirror to the adjoining wall. But when his wife Luanne walked in and looked at the job she said, “It’s not straight.”

“That can’t be,” said Mitchell. “I know these walls are vertical because I double checked them with a level and with a plumb line. I measured from the left edge of the mirror to the wall in two places, both 40 cm. And I also checked to make sure that the mirror is a perfect rectangle. The wall is vertical. The left edge of the mirror is parallel to the wall. The right edge of the mirror is parallel to the left edge. It’s straight.”

“Well,” said Luanne, “I’m looking at the right edge of the mirror and it isn’t vertical.”

Who’s right, Mitchell or Luanne?

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