axioms: Some rules about a collection of objects S's structure.
statement: An assertion that is either true or false.
proof: A convincing argument about the acuracy of a statement.
proposition: an statement can be proved to be true.
theorem: a proposition of major importance.
lemmas:
corollaries:
1.2 Set and Equivalence Relations
Defintion:
set: is a well-defined collection of objects; that is, it is defined in such a manner that we can determine for any given object $x$ whether or not $x$ belongs to the set.
free text book: http://abstract.ups.edu/download/aata-20170805.pdf
1 Preliminaries
1.1 proofs
Definition:
1.2 Set and Equivalence Relations
Defintion: