ACM Copyright notice
Permission to make digital or hard copies of part or all of this work
for personal or classroom use is granted without fee provided that
copies are not made or distributed for profit or direct commercial
advantage and that copies bear this notice and the full citation on
the first page. Copyrights for components of this work owned by others
than ACM must be honored. Abstracting with credit is permitted. To
copy otherwise, to republish, to post on servers, or to redistribute
to lists, requires prior specific permission and/or a fee. Request
permissions from Publications Dept, ACM Inc., fax +1 (212) 869-0481,
or
(permissions@acm.org).