[Mathematic Form 4] Classified

A SET is a well-defined group of objects, or a collection of objects that have a common property.

Objects in a set are called members or elements of the set.

Sets can be defined either by description, or set notation with braces { } .

Eg:
By description, P is a set of consonants in the word "EXCELLENT".
By set notation with braces, P = { consonants in the word "EXCELLENT"} or
P = {x:x is a consonant in the word "EXCELLENT"} or
P = {X, C, L, N, T}

(Note the use of commas, and non-repetition of the same elements in the set, i.e. the letter "L")