propp: 'concl' patterns;
assumptions: tactics for non-goal export;
use Display.pretty_thm_no_hyps;
assm vs. assume vs. presume;
tuned type goal;
tuned print_goal;
relative exports, absolute export_thm rule;
transfer_facts;
tuned;
by(induct_tac "b" 1);
by(Auto_tac);