Re: Trademark, not Patent.
Looking for prior art is (mostly) associated with patents. I'm pretty sure the "famous Czech Branching Movie" ("Dream Machines/Computer Lib", Ted Nelson) from 1967 predates the examples mentioned so far, as do the IBM "Programmed Learning" books I first met in 1961 or so.
The issue isn't the technique, but the name. Having a character named Ricky Rat may skate close to the edge, but using the M-words is gonna cost you.
Biting the hand that feeds IT
