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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 _verify_cartesian(s, t):
 """Verifies that a point is in the reference triangle. I.e., checks that they sum to <= one and are each non-negative. Args: s (float):
 Parameter along the reference triangle. t (float):
 Parameter along the reference triangle. Raises: ValueError: If the point lies outside the reference triangle. """

        if s < 0.0 or t < 0.0 or s + t > 1.0:
            raise ValueError("Point lies outside reference triangle", s, t)