Wolfram Research
Wolfram Math World: Sets
This page discusses sets and set theory in mathematics and probability, and it discusses the notation and properties of sets.
Other
Appalachian State University: Sets and Bags
This page provides extensive information about sets and bags. Includes descriptive set notation and examples.
OpenStax
Open Stax: Catherine Schmidt Jones: Keys and Scales Are Sets
Help your students identify sets and intersections of sets with this musical activity. Using the concept of key signatures, students will learn that scales are sets of notes. Included with this lesson plan are downloadable worksheets and...