Four

How to type it

Left index finger. Introduced in Lesson 20: Numbers: 1 to 5.

Common uses

• Four is the traditional number of seasons and of cardinal compass directions.
• A quarter is one of four equal parts.

Less common uses

• In China, Japan, and Korea, 4 is considered unlucky because its spoken name sounds like the word for death.
• The four color theorem, proved with computer help in 1976, says four colors suffice so that no two bordering regions on a map match.