LIST    ( n - ) List screen n and set SCR to contain n.
LOAD    ( n - ) Interpref screen n, then resume interpretation of the current input stream.
SCR ( - ad dr ) System variable containing screen number most recently listed.
BLOCK   ( n - addr )    Leave memory address of block, reading from mass storage if necessary.
UPDATE  ( - )   Mark last block referenced as modified.
BUFFER  ( n - addr )    Leave addr of a free buffer, assigned to block n, write previous contents to mass storage if UPDATEd
SAVE-BUFFERS    ( - )   Write all UPDATEd blocks to mass storage.
EMPTY-BUFFERS   ( - )   Mark all block buffers as empty, without writing UPDATEd blocks to mass storage.

