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This module implements the Residue function and related tools for working
with residues.
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    Finds the residue of ``expr`` at the point x=x0.

    The residue is defined as the coefficient of 1/(x-x0) in the power series
    expansion about x=x0.

    Examples
    ========

    >>> from sympy import Symbol, residue, sin
    >>> x = Symbol("x")
    >>> residue(1/x, x, 0)
    1
    >>> residue(1/x**2, x, 0)
    0
    >>> residue(2/sin(x), x, 0)
    2

    This function is essential for the Residue Theorem [1].

    References
    ==========

    1. http://en.wikipedia.org/wiki/Residue_theorem
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