&[(1971, 12, 31),(1972, 6, 30),(1972, 12, 31),(1973, 12, 31),(1974, 12, 31),(1975, 12, 31),(1976, 12, 31),(1977, 12, 31),(1978, 12, 31),(1979, 12, 31),(1981, 6, 30),(1982, 6, 30),(1983, 6, 30),(1985, 6, 30),(1987, 12, 31),(1989, 12, 31),(1990, 12, 31),(1992, 6, 30),(1993, 6, 30),(1994, 6, 30),(1995, 12, 31),(1997, 6, 30),(1998, 12, 31),(2005, 12, 31),(2008, 12, 31),(2012, 6, 30),(2015, 6, 30),(2016, 12, 31)]