general_fact: 4 is the number of strings on a violin, a viola, a cello, double bass, a cuatro and a ukulele, and the number of string pairs on a mandolin.
math_fact: 4 is the smallest number of colors sufficient to color all planar maps.
trivia: 4 is the maximal number of horses in one row for carriage.
historical_date: January 4th is the day in 1965 that United States President Lyndon B. Johnson proclaims his "Great Society" during his State of the Union address.