Let
be stably embedded
in a structure
.
We consider
Fubini measures on the subcategory
of the category
of definable
sets in
,
with “Fubini” signaling good behavior in definable families. We show that
such a Fubini measure extends uniquely to the larger subcategory of
whose objects are the sets that are “fiberable over
”. In cases of interest “fiberable
over
” coincides with
“co-analyzable relative to
”.
This applies in particular to the differential field
of transseries
with
,
and to differentially closed fields with constant field
.