Editing Cyc (section)

==Knowledge base==
The [[knowledge base]] is divided into ''microtheories''. Unlike the knowledge base as a whole, each microtheory must be free from monotonic contradictions. Each microtheory is a first-class object in the Cyc ontology; it has a name that is a regular constant. The concept names in Cyc are CycL ''terms'' or ''constants''.<ref name=":2" /> Constants start with an optional <code>#$</code> and are case-sensitive. There are constants for:
* Individual items known as ''individuals'', such as <code>#$BillClinton</code> or <code>#$France</code>.
* ''Collections'', such as <code>#$Tree-ThePlant</code> (containing all trees) or <code>#$EquivalenceRelation</code> (containing all [[equivalence relation]]s). A member of a collection is called an ''instance'' of that collection.<ref name=":3" />
* ''Functions'', which produce new terms from given ones. For example, <code>#$FruitFn</code>, when provided with an argument describing a type (or collection) of plants, will return the collection of its fruits. By convention, function constants start with an upper-case letter and end with the string <code>Fn</code>.
* ''Truth functions'', which can apply to one or more other concepts and return either true or false. For example, <code>#$siblings</code> is the sibling relationship, true if the two arguments are [[sibling]]s. By convention, truth function constants start with a lowercase letter.
For every instance of the collection <code>#$ChordataPhylum</code> (i.e., for every [[chordate]]), there exists a female animal (instance of <code>#$FemaleAnimal</code>), which is its mother (described by the predicate <code>#$biologicalMother</code>).<ref name=":3" />