Pruning based on word pairs is performed in the initial stage of parsing, before any structure is built above the words. Some parts of the sentence will be excised and made into modifiers after building of structure has commenced - negation, adverbs, prepositional phrases, parenthetical phrases, etc., - causing new word pairs to appear after removal of the modifiers. The NOTWITH operator is necessary, both to prevent errors being made due to insufficient pruning in the initial stage, and to re-initiate pruning at the word-pair level after excision, and while some structure may already exist above the words.

The problem:

John is not going home.

John is certainly not a crackpot.

The "is" can be a verb auxiliary or the present tense of the verb "to be". The PARSE operator between the "is" and the "not" or "certainly" can’t see past them, and would put out both alternatives – Verb Auxiliary or Present Tense. Present Tense would cause the alternative EndVerbPhrase, which means we could already have built VerbPhrase around "is" before the "not" or the adverb is removed and the PARSE can see the Present Participle or the Article.

The statement

ALTERNATIVES(EndVerbPhrase,{NOTWITH(VerbAuxiliary,{BaseForm, PresentTense, PastTense}))

prevents the alternative of EndVerbPhrase being reached if VerbAuxiliary is still a possible alternative. When the "not" is moved to be a modifier, the proximity of the Verb Auxiliary and the Present Participle removes the PresentTense alternative, whereas an article or noun would remove the VerbAuxiliary alternative.

Instead of a single alternative not being present, a list of forbidden alternatives can be used, as

ALTERNATIVES(EndVerbPhrase,{NOTWITH(ForbiddenAlternatives%,{BaseForm, PresentTense, PastTense}))

Any one of the alternatives in ForbiddenAlternatives% being present will prevent the alternative provided by the symbol (EndVerbPhrase) being reached.

This blocking means that a reduction in alternatives coming in one side (Pins 2 or 3) of the PARSE operator can lead to an increase in alternatives coming out of Pin 1 of the operator, necessitating the alternatives being killed to propagate properly.

NOTWITH is part of an apparatus that seeks to make activation and inhibition of equal facility.


Related Operators