HOL is an abbreviation for Higher order logic[?], a branch of symbolic logic in which statements can be quantified over objects, predicates, predicates of predicates etc.
... 1796, 1800, 1804, 1808, 1812, 1816
Source: U.S. Office of the Federal Register (http://www.archives.gov/federal_register/electoral_college/scores.html#1804)
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