User:Rschwieb/Requiring identity table

* Northcott does not include unity in the definition of ring, but notes that rings in the text should be assumed to have unity.

* Smith & Romanowska have definition 1.3.1 "'ring' or 'unital ring' or 'ring-with-1'", and definition 1.3.2 "'ring' or 'non-unital ring' or 'ring-without-1'" and instruct to "determine from context".