triangle inequality for naturals and integers #177
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On Dr. Escardo's invitation from mathstodon, I am contributing my proof of the triangle inequality in the Naturals and the Integers. In the Naturals, I define a new Absolute Difference operation and prove some elementary lemmas. I then add associated lemmas for Absolute Difference to the Natural Order lemmas, proving the triangle inequality on the way for the naturals under this operation. I then prove some useful lemmas for Absolute Value in the Integers related to this new operation, and conclude by proving the triangle inequality in the Integer Order file (for both abs and adding a translated lemma to absZ for convenience).