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v. 1. Western Europe -- v. 2. Slavic -- v. 3. Eastern Europe -- v. 4. Spanish Portuguese, Philippine, Basque -- v. 5. Mid-East, Far-East, Scandinavian, English language, American Indian, international -- v. 6. Artist index, titl index -- v. 7. Record number index, matrix number index.
Rahkonen et al. (Mon,) studied this question.