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This is for the case where your Ring[T] is a Rng (i.e. there is no unit).
http://en.wikipedia.org/wiki/Pseudo-ring#Adjoining_an_identity_element
This is for the case where your Ring[T] is a Rng (i.e. there is no unit).
http://en.wikipedia.org/wiki/Pseudo-ring#Adjoining_an_identity_element