The language of addition

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Across
  1. 3. m+(r+q)=(m+r)+q
  2. 6. ()
  3. 7. word that tell us to add
  4. 8. another word that tells us to add
  5. 9. the answer in addition
Down
  1. 1. 7+6+6+7
  2. 2. identity x+0=X
  3. 3. 2+3=5 the 2 & 3 are the__
  4. 4. =
  5. 5. grafica
  6. 6. +