 Solution

ID: past-exam-of-the-mathematics-course-of-the-year-2-of-the-natural-sciences-course-of-the-university-of-cambridge/2010/paper-1/7/iii/solution

\nabla v = (- u_{y}, u_{x})

\nabla u = 0 ⟺ \nabla v = 0.

Thus their stationary points coincide, including degenerate ones.

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