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).