Let | x denote all steamers, or steam-vessels, |

y denote all armed vessels, | |

z denote all vessels of the Mediterranean. |

(1) That there are no armed vessels except steamers in the Mediterranean.

(2) That all unarmed steamers are in the Mediterranean (since the
steam-vessels not of the Mediterranean are armed). Hence we infer
that *the vessels of the Mediterranean consist of all unarmed
steamers; any number of armed steamers; and any number of unarmed
vessels without steam*. This, expressed symbolically, is equation
(15).