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Error Estimates for Finite Element Approximation to Elliptic Optimal Control Problems With Boundary Observations in $H^{-\frac{1}{2}}(\Gamma)$. Adv. Appl. Math. Mech. 2024, 16 (5), 1152-1175. https://doi.org/10.4208/aamm.OA-2022-0172.