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Let $X$ be a non-singular projective surface over an algebraically closed field $ \mathbb{K} $. If $D$ is an effective divisor on $X$, $ p_{a} = 1 - \chi(\mathcal{O}_{D}) $ is its arithmetic genus and $ K $ is a canonical divisor on $X$, show that \[ 2p_{a} - 2 = D.(D+K) \]