removed cases_of;
renamed cases_tac to case_tac; tuned to work with basic HOL as well;
add_cases_induct: proper case names;
adapted to new PureThy.add_thms etc.;
Last = List +
consts last :: 'a list => 'a
recdef last "measure (%xs. length xs)"
"last [x] = x"
"last (x#y#zs) = last (y#zs)"
end