TITLE: Formally prove that every finite language is regular
QUESTION [9 upvotes]: I know how to prove this informally, but don't know what the formal proof should look like.

REPLY [4 votes]: Another definition of a regular language is one generated by a regular grammar. If $L = \{v_1, v_2, \dots , v_n\}$ then
$$S \to v_1 \\ S \to v_2 \\ \vdots \\S \to v_n$$
is a regular grammar of $L$.