Reified NATs are another type of constant. A constant is one type of term . CycL derives from first-order predicate calculus , but includes many extensions to FOPC which enhance the expressiveness of the language. For a more complete description of CycL, click here . A formula is an expression in a formal language that makes some declarative statement about the world.
Formulas are analogous to declarative sentences in English.
In CycL, formulas that are well-formed are called CycFormulas. A formal language incorporating predicate symbols, function symbols, constant symbols, variables, logical connectives and quantifiers, which can be used to express facts about a world. Unlike propositional logic, FOPC can express general statements or statements about existence, by using quantified variables. Functions in CycL are also single-valued. They can be applied to arguments to form non-atomic terms , which can then appear in formulas as an argument to a predicate.