---
title: "Left corner"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Left_corner"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:35:27.302672+00:00"
instance: "kb-cron"
---

In formal language theory, the left corner of a production rule in a context-free grammar is the left-most symbol on the right side of the rule.
For example, in the rule A→Xα, X is the left corner.
The left corner table associates to a symbol all possible left corners for that symbol, and the left corners of those symbols, etc.
Given the grammar

S → VP
S → NP VP
VP → V NP
NP → DET N
the left corner table is as follows.

Left corners are used to add bottom-up filtering to a top-down parser, or top-down filtering to a bottom-up parser.


== References ==