\ Btree of BtSet's                                                   vandys
only extensions definitions

Btree -> subclass: BtBtSet

BtBtSet -> :method ! ( ... self -- )   1 abort" Bad API use" method;
BtBtSet -> :method @ { key self -- btset }
   key self super-> @ if exit then
   BtSet -> new dup { btset } key self super-> !   btset method;
BtBtSet -> :method in? ( key self -- ? )
   super-> @ dup if nip then method;