As I understand, he uses both "intention" and "intension". "Intention" as a desire to do something, and "intensional" as opposite of "extensional": https://www.collinsdictionary.com/dictionary/english/intensi...
Ooops, thanks for catching, typo fixed. That Tree Calculus is intenSional (https://plato.stanford.edu/entries/logic-intensional/) is one of its main selling points, so that spelling must've rewired too many motor neurons.
(It’s also likely that this minor error is spawned by the use of intension, a very uncommon word, in the description of Tree Calculus.)