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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def clean(self: 'TSelf', *, atol: float=1e-9) -> 'TSelf': """Remove terms with coefficients of absolute value atol or less."""

        negligible = [v for v, c in self._terms.items() if abs(c) <= atol]
        for v in negligible:
            del self._terms[v]
        return self