= Solution
A <removable singularity> is an <isolated singularity> for which the function on the punctured disk extends to a <holomorphic function> on the full disk, by assigning or correcting its value at $a$. In <Laurent series> terms,
$$
\boxed{c_j=0\text{ for every }j<0.}
$$
The remaining power series defines the extension with value $c_0$ at $a$. Conversely, a holomorphic extension has a <Taylor series> there, so uniqueness of the <Laurent series> forces all negative coefficients to vanish.
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