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NIntegrate[(Cos[20 x] - Cos[19 x])/(1 - (Cos[x] + Cos[y])/2), {x, -Pi, Pi}, {y, -Pi, Pi}]
NIntegrate[(Cos[20 x] - Cos[19 x])/(1 - (Cos[x] + Cos[y])/2), {x, -Pi, Pi}, {y, -Pi, Pi}]
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