An LL parser or Left-to-right, leftmost derivation parser, is a top down parser for a restricted context free language. This visualizer shows an LL(1) parser which has one lookahead in form FIRST and FOLLOW sets. The FIRST set of a nonterminal NT, FIRST(NT), is the set of terminals that can be the first element of any string derived from NT. FOLLOW(NT) is a set of terminals that can appear immediately to the right of NT in any derivation. LL(1) grammars must not have certain conflicts, such as FIRST/FIRST conflicts, left recursion, and FIRST/FOLLOW conflicts.