maybe narrowing does not need exp_preserves_sub? implement narrowing/case has_pr
remaining cases of narrowing, problem:

in case subtyp_bind, the decs might have non-collapsed bounds, but we put them into env
induction scheme for narrowing, narrowing probably does not need exp_preserves_sub
induction scheme for exp_preserves_sub_pr
garbage collection deleted 1263 useless lines
move soundness proof to the end of the file
moving