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explain krta ho B1 B2 BM (cannot merge) c3 c4 // del c3 and c4 c4 c2 c2 c3 missing c1 c1 c2 c1 ------------------------------------------------- B1 B2 BM (can merge) c4 c3 c3 c4 c2 c2 c3 not missing c1 c1 c2 c1