How is the inequality x less than or equal to 1 written in interval notation?

1. Every number to the left of 1 works, and 1 itself works too. 2. An included endpoint takes a bracket, so 1 is written with a bracket. 3. There is no lower end, so negative infinity opens the interval. _Source: OpenStax Intermediate Algebra (CC BY 4.0), Ch 2 "Solving Linear Equations", section 2.5 Solve Linear Inequalities_