replaced generic 'hide' command by more conventional 'hide_class', 'hide_type', 'hide_const', 'hide_fact' -- frees some popular keywords;
no_document use_thy "Setup";
no_document use_thys ["Efficient_Nat"];
use_thy "Introduction";
use_thy "Program";
use_thy "Adaptation";
use_thy "Further";
use_thy "ML";