Residue at infinity
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In complex analysis, a branch of mathematics, the residue at infinity is a residue of a holomorphic function on an annulus having an infinite external radius. The infinity is a point added to the local space
in order to render it compact (in this case it is a one-point compactification). This space denoted
is isomorphic to the Riemann sphere.[1] One can use the residue at infinity to calculate some integrals.