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Directory:Jon Awbrey/Papers/Peirce's 1870 Logic Of Relatives (view source)

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Peirce next takes up the action of the "number of" map on the two types of, loosely speaking, ''additive'' operations that we normally consider in logic.

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The sign <math>^{\backprime\backprime} + ^{\prime\prime}</math> denotes what Peirce calls "the invertible addition", corresponding to the exclusive disjunction of logical terms or the symmetric difference of their extensions as sets.

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This is why Peirce trims his discussion of this point with the following hedge:

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Finally, a morphism with respect to addition, even a contingently qualified one, must do the right stuff on behalf of the additive identity:

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Jon Awbrey

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