Homography

In mathematics, the characteristic sequence of a given sequence s is a sequence of 1s and 0s which tells which elements of s are in some set.

Given two sets $A\subseteq B$ and a sequence s = $⟨s_n:n\in \mathbb{\mathbb{N}}⟩$ of elements of $B$, the characteristic sequence of $s$ is the sequence $⟨c_n:n\in \mathbb{\mathbb{N}}⟩$ defined so that $c_n=1$ if and only if $s_n\in A$:

$c_n=\{\begin{array}{ll}0& s_n\in ̸A,\\ 1& s_n\in A.\end{array}$

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