Left Corner

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 a symbol with 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
Symbol Left corner(s)
S VP, NP, V, DET
NP Det
VP V

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

You can use the left corners to do top-down filtering of a bottom-up parser.

Famous quotes containing the words left and/or corner:

    “It’s no accident that of all the monuments left of the Greco- Roman culture the biggest is the ballpark, the Colosseum, the Yankee Stadium of ancient times.”
    —Walter Wellesley (Red)

    “Something is sticking out its tongue at me from the corner of my mirror.”
    —Mason Cooley (b. 1927)