A proof is a sequence of logical deductions that establishes the validity of a mathematical statement.

For the specific 6120a discrete mathematics and i could not find information about it , can you provide more context about it, what topic it cover or what book it belong to .

A set is a collection of objects, denoted by $S = {a_1, a_2, ..., a_n}$, where $a_i$ are the elements of $S$.

Propositional logic is a branch of logic that deals with statements that can be either true or false. Propositional logic is used extensively in computer science, as it provides a formal framework for reasoning about Boolean expressions and logical statements.

A set $A$ is a subset of a set $B$, denoted by $A \subseteq B$, if every element of $A$ is also an element of $B$.