What Lisp would that be? Considering it is not (as far as I can see) mentioned in McCarthys History of Lisp (https://dl.acm.org/doi/pdf/10.1145/800025.1198360 h

What Lisp would that be? Considering it is not (as far as I can see) mentioned in McCarthys History of Lisp (https://dl.acm.org/doi/pdf/10.1145/800025.1198360 https://dl.acm.org/doi/pdf/10.1145/800025.1198360) I think no actual Lisp used unary arithmetic based on list lengths. Sure, there might be toy examples used for teaching that did this, but that is a something different.