Some half dozen persons have written technically on combinatory logic, and most of these, including ourselves, have published something erroneous.

Since some of our fellow sinners are among the most careful and competent logicians on the contemporary scene, we regard this as evidence that the subject is refractory.

Thus fullness of exposition is necessary for accuracy; and excessive condensation would be false economy here, even more than it is ordinarily.

Haskell B. Curry and Robert Feys, Preface to “Combinatory Logic”