PHL246H1 Lecture Notes - Kathleen Wynne, Empty Set, Bracket
Document Summary
Intuitively, a set is a collection of objects (things, entities). For instance, the set t of people teaching this course is the collection of objects (or subjects, if you prefer) that is either a ta for phl 246 or an instructor for phl 246. We use curly brackets {" and }" to denote sets. One way to describe t is as follows: t = {parisa, seya, franz}. A different way to describe the very same set t is as follows: t = {x: x is a ta for phl 246 or x is an instructor for phl 246}. The order in which the members are listed does not matter: t = {parisa, seya, franz} = {seya, parisa, Nor does it matter if a member is listed once or more than once: t = {parisa, seya, franz} = {seya, parisa, Every set c is identical to the set of all its members: for all sets c, c = {x: x c}.
