substantial speedup of assumption and elim-resolution: Logic.assum_problems refrains from eager application of parameters, discriminate via Term.could_unify before invoking full unification (assumes terms in beta-normal form, as do higher term net operations anyway);
By chapter:
chapters 1 and 2, maybe 3: Peter White
chapters 6, 7 and 8: David von Oheim
chapter 6, maybe 8: Gerwin Klein
chapters 3, maybe 4: Tanja Vos
chapters 1-3 at least: Stefano Bistarelli