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Article Contents

ABSTRACT

1.INTRODUCTION

2.PREVIOUS OBSERVATIONS

3.THEORY
3.1.Metal-poor HB hypothesis
3.2.Metal-rich HB hypothesis
3.3.Metal-poor or metal-rich HB?

4.ISSUES
4.1.alpha-enhancement
4.2.EHB stars in star clusters
4.3.Binaries
4.4.Other issues

5.GALEX OBSERVATIONS

6.NEW ISSUE: ENHANCED-HELIUM POPULATION

7.NEW ISSUE: UV-BRIGHT GLOBULAR CLUSTERS IN M87

8.CONCLUSIONS

REFERENCES