13.3 Atoms: Their Types and Weights 251 13.3.3 Logical Links There is a host of link types embodying logical relationships as defined in the PLN logic system, e.g. e InheritanceLink e SubsetLink (aka ExtensionalInheritanceLink) e Intensional InheritanceLink which embody different sorts of inheritance, e.g. SubsetLink salmon fish IntensionalInheritanceLink whale fish InheritanceLink fish animal and then e SimilarityLink e ExtensionalSimilarityLink e IntensionalSimilarityLink which are symmetrical versions, e.g. SimilaritytLink shark barracuda IntensionalSimilarityLink shark dolphin ExtensionalSimiliarityLink American obese\_person There are also higher-order versions of these links, both asymmetric e ImplicationLink e ExtensionallmplicationLink e IntensionallmplicationLink and symmetric e EquivalenceLink e ExtensionalEquivalenceLink e IntensionalEquivalenceLink These are used between predicates and links, e.g. ImplicationLink EvaluationLink eat ListLink $X dirt EvaluationLink tee. ListLink $X sluok or HOUSE_OVERSIGHT_013167