under_elem -> elem_at; loop_tup_types optimization; rref_of + gcc bug
Revert "README - building"

This reverts commit a0dab4bf1ba8713658d25f04c20839384a1a692c.
Revert "under_elem -> elem_at; loop_tup_types optimization; rref_of + gcc bug"

This reverts commit e67745c8f2b093b4efaccf5065bd3e2be3531637.
under_elem -> elem_at; loop_tup_types optimization; rref_of + gcc bug