<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman, new york, times, serif;font-size:12pt"><DIV>Hi </DIV>
<DIV>can anyone refer me to some literature about history of acoustic sum rules? i mean when was it proposed for the first time? and it's versions known here as "simple" and "crystal"? </DIV>
<DIV>Thank You</DIV></div><br>
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