Typofix add pure

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
Checkpoint

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
Start prenexifying

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
Fix example.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>
OK, prenex

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>