Minor Inside the current revision of the proposal for an OData Delta Query Protocol i.e. [OData Delta Query Protocol Design 2012-12-19.docx](https://www.oasis-open.org/committees/download.php/47755/OData%20Delta%20Query%20Protocol%20Design%202012-12-19.docx) the term tombstone should IMO better be introduced before its first appearance on page 6 (result maintenance and atom format describing sections).
I suggest to do this inside the section "Delta Responses" on pages 3 or 4 since it is simply a "deleted-link" with a cooler name, right? ... which is part of the response and not the request.
Update:
Old proposal was to "Define the term tombstone (virtual entity handle for deleted entities) before using it."
Following the feedback in a comment by Mike it is now proposed to replace instead (as addressed in upcoming revision).
Addressed in version 1.3 by removing the use of "tombstone" and consistently using "deleted entry". It is a cooler name, but not worth introducing a separate concept 
Thanks a lot Mike for changing this already (in the upcoming revision) by replacing all tombstones with deleted entries.
Otherwise we might have opened a can of worms, since in some cultures, tombstones tend to attract additional stones on top, which would have implied the potential need of special structures describing these Collections. Dealing with the loss of an entry is hard enough
Update: I acknowledge the issue as applied in the current revision [OData Delta Query Protocol Design 2013-1-23.docx](https://www.oasis-open.org/committees/download.php/47996/OData%20Delta%20Query%20Protocol%20Design%202013-1-23.docx) .
Readability of summary