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**1. Homework Statement**

Can someone please explain to me how umklapp processes K_1 +K_2 = K_3 +G where G is nonzero conserve momentum? I have read the explanation in Kittel over and over and I just don't understand. I also read https://www.physicsforums.com/showthread.php?t=165385 so don't just give me a link to that.

**2. Homework Equations**

**3. The Attempt at a Solution**