... population.¹

As an exercise you might want to see if you can derive the corresponding equations for $x_{12}'$ and $x_{22}'$.

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... equations.²

And you thought that dealing with one was bad enough!

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... fertilities.³

Fortunately, it takes rather weird fertility schemes to produce such a result.

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....⁴

There's a reason for doing this called Bateman's principle that we can discuss, if you'd like.

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