Professor L. Wilson's Crossword Puzzle

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Across
  1. 1. makes fractions the smallest they can be.
  2. 5. Down in the ground.
  3. 7. It makes the world a better place
Down
  1. 2. up and down, side to side.
  2. 3. What makes a multiple?
  3. 4. L x W
  4. 6. Heaven.