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\begin{align*} v+r-e &= (v_1 + v_2) + (r_1 + r_2 - 1) - (e_1 + e_2 + 1) \\ &= (v_1 + r_1 - e_1) + (v_2 + r_2 - e_2) - 2 \\ &= 2+2-2 \\ &= 2 \end{align*}