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It is essential to read a rule given for a date carefully. The Easter Act of 1928 defines a potential fixed date for Easter in England, for example, as the first Sunday after the second Saturday in April. Careless writers have occasionally stated that this rule is the second Sunday in April. The two rules are not equivalent. For any year in which 1 April falls on a Sunday, for example, the second Saturday would fall on 14 April. The second Sunday would then fall on 8 April, but the Sunday after the second Saturday would fall on 15 April. |
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2.4.) The Nth DOW before or after some other base date. |
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2.4.1.) Immovable base date. Use the Nth-DOW-before or -after rule after obtaining the base date using the fixed-date rule. The example of the appearance date of Sinterklass on the Saturday preceding 6 December results in: |
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date1 = saint_nicholas (year);
date2 = Nth_DOW_before_date (1, DOW_SATURDAY, &date1); |
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where saint_nicholas () returns 6 December, since that is the designated saint's day. |
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Note that the use of utility routines is part of the solution to avoiding the problem of regressive definition and function deadlock. |
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2.4.2.) The base date is a movable feast. |
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2.4.2.1.) The movable feast is defined by its DOW. Determine the date of the movable feast, and use the days-after or days-before rule. Most of the days in the Easter cycle are determined in this way. The given example of the appearance of the Tutti-men on the second Tuesday after Easter results in: |
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date1 = easter (year);
date2 = date_N_days_after_date (9, &date1); |
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since the second Tuesday must fall exactly nine days after Easter, which must fall on a Sunday. |
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2.4.2.2.) The movable feast is not defined by its DOW. Use the Nth-DOW rule, after obtaining the base date. The example of the first Monday after Chinese New Year would result in: |
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date1 = chinese_new_year (year);
date2 = Nth_DOW_after_date (1, DOW_MONDAY, &date1); |
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2.5.) The DOW closest to a date. Use the closest-DOW rule. The example of Advent Sunday, defined as ''the Sunday of, or nearest to, Saint Andrew's Day" results in: |
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