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The porism is a term whose precise definition is difficult to pin down.

It arises from the works of Euclid, and appears to have two different meanings:

  1. A result which follows directly, or in passing, during the course of proving something else; that is, a corollary.
  2. A proposition that asserts that there may be conditions under which a particular problem has either no solutions or an indeterminate number of them.

Linguistic Note

The word porism derives ultimately from the Greek $\pi \omicron \rho \omicron \varsigma$ (poros) meaning a thing brought, or a thing deduced.