 In 1942, Fitch introduced a logic that he labeled \(K\). The expressions in \(K\) are formed like combinatory terms by a binary application operation, which is not assumed to be associative. (See the definition of combinatory terms in the next section.) However, the constants of \(K\) do not coincide with the constants of pure CL. Fitch uses 10 constants: \(\varepsilon\), \(o\), \(\acute{\varepsilon}\),  \(\acute{o}\), \(W\), \(=\), \(\land\), \(\lor\), \(E\)  and \(*\). The first five constants are combinators, though the notation may suggest a different (informal) meaning. ‘\(=\)’ is the syntactical identity of expressions. ‘\(\land\)’ and ‘\(\lor\)’ are intended to stand for “and” and “or.” ‘\(E\)’ is the analogue of Schönfinkel’s  \(U\), but it corresponds to a non-vacuous existential quantifier. Finally, ‘\(*\)’ is similar to the transitive closure operator for binary relations or the Kleene star. Notably, there is no negation or universal quantifier in the system. The uses of the constants are characterized as follows—somewhat like axioms characterize combinators.