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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 _approx_eq_(self, other: Any, atol: float) -> bool: """Checks whether two linear combinations are approximately equal."""

        if not isinstance(other, LinearDict):
            return NotImplemented

        all_vs = set(self.keys()) | set(other.keys())
        return all(abs(self[v] - other[v]) < atol for v in all_vs)