13.3 Atoms: Their Types and Weights 249
Note that SubsetLink refers to a purely extensional subset relationship, and that Inheri- tanceLInk should be used for the generic "intensional + extensional" analogue of this — more on this below. SubsetLink could more consistently (with other link types) be named Extension- alInheritanceLink, but SubsetLink is used because it’s shorter and more intuitive.
There are links representing Boolean operations AND, OR and NOT. For instance, we may say ImplicationLink
ANDLink ConceptNode young
ConceptNode beautiful ConceptNode attractive
or, using links and VariableNodes instead of ConceptNodes,
AverageLink $X ImplicationLink ANDLink EvaluationLink young $X EvaluationLink beautiful $x EvaluationLink attractive $X
NOTLink is a unary link, so e.g. we might say
AverageLink $X ImplicationLink ANDLink EvaluationLink young $X EvaluationLink beautiful $x EvaluationLink NOT EvaluationLink poor $X EvaluationLink attractive $X
ContextLink allows explicit contextualization of knowledge, which is used in PLN, e.g.
ContextLink ConceptNode golf InheritanceLink ObjectNode BenGoertzel ConceptNode incompetent
says that Ben Goertzel is incompetent in the context of golf.
13.3.2 Variable Atoms
We have already introduced VariableNodes above; it’s also possible to specify the type of a VariableNode via linking it to a VariableTypeNode via a TypedVariableLink, e.g. VariableTypeLink
VariableNode $X
VariableTypeNode ConceptNode which specifies that the variable $X should be filled with a ConceptNode.
Variables are handled via quantifiers; the default quantifier being the AverageLink, so that the default interpretation of
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