When talking about J forks, the author says they don't know how to parse `x (f1 f2 f3 f4 f5) y`. After reading the relevant documentation, I believe this parses as
(x f1 y) f2 ((x f3 y) f4 (x f5 y)) (x f1 y) f2 ((x f3 y) f4 (x f5 y)) x f1 ((f2 y) f3 ((f4 y) f5 (f6 y)))