(Urgent:) Getting start and end translation-timestep of a (hairpin) grob

[Urs Liska]

Hi,

this is related to my previous thread and particularly to the file 
attached to
http://lists.gnu.org/archive/html/lilypond-user/2015-04/msg00263.html

If I have a Scheme engraver listening to TextScript-s I can get a list 
of entries at the same timestep and then compare them for equality.
This even works without changes for DynamicText because that also has a 
'text property. But if i have spanners such as hairpins it's not that 
simple anymore. So I'm asking myself if I can access the starting and 
ending timesteps of hairpins that are present in such a list. Of course 
I can collect hairpins in a list like I can collect TextScripts 
(currently I'm listening for line-interface). But is it possible to 
retrieve the start *and* end position of such items?

The goal is to iterate over the list and find matching hairpins to 
remove duplicate ones.

Thank you very much in advance
Urs