doc-src/Tutorial/Datatype/abgoalind.ML

deleted "escape" and "trim"; Basis Library can do string escapes if necessary

Goal
 "evala env (substa s a) = evala (%x. evala env (s x)) a & \
\ evalb env (substb s b) = evalb (%x. evala env (s x)) b";
by(mutual_induct_tac ["a","b"] 1);