Years of the set of category year one is { 0,4,8,...,1996,2000,2004,...} Years of the set of category year two { 1,5,9,...,1997,2001,2005,...} and {2,6,10,...,1998,2002,206,...}. Years of the set of category year three is { 3,7,11,...,1999,2003,2007,...}

1. Ethiopia’s calendar is neither ancient nor new
because it is an eternal image of tropics and sun.
 Therefore, it brings three categories of four
years.
Category A is the first year that begins a day late. New
Year begins on Meskeram 1, when September is 12.
Category B is the second and third years that each of them
has similar beginning and ending days. New Year of each
begins on Meskeram 1, when September is 11; and ends on
Pagume 5, when September is 10.
Category C is the fourth year that ends by a day more. This
category three is traditionally known as leap year. This year
begins on Meskeram 1, when September is 11 and ends on
Pagume 6, when September is 11.
Categories A and B are subset of four years that each year has a
period of 365 days.
 And category C is a subset of four years that has a period of 366
days.