Symbol k^L

The passage around this formula

Take the genotype-space reading, which is the one that empirical work now uses. A genotype is a sequence. The map is $w \colon \mathcal{G} \to \mathbb{R}, \qquad |\mathcal{G}| = k^{L}$. where the sequence has some length and each site takes one of a small number of states. Two genotypes are neighbours when they differ at a single site. This is the object Maynard Smith described as protein space, and his framing remains the cleanest statement of the constraint: evolution must move through the space one step at a time, and every intermediate must itself be viable, in the way that changing WORD to GENE one letter at a time requires each intervening string to be a real word [ 4 ] .

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