The modified first step: the modified core is indifferent to empty boundary members #
The counterpart, for boundary members, of the empty blow-up convention [Kol07, 32], for the modified
first step of [Wlo09, Theorem 7.4.1]: deleting empty members of the boundary along an order
embedding e : F'.ι ↪o E.ι of the index types does not change the modified core at a kept member.
This is the counterpart of BDan.coreFamOn_indifferentToEmptyMembers without the first blow-up.
The stopped locus and H⁺ of the member e i of E are those of the member i of F'
(hplus_withBoundary: the same set E^{e i} = F'^i and the same ideal), so the two modified cores
are read on the same closed hypersurface (coreModOn_eq_of_eq); the two restricted triples have the
same ideal (the pull-back of 𝓘 along the same inclusion) and boundaries, the traces of
E − E^{e i} and of F' − F'^i, which correspond along e with the deleted members empty, so the
indifference of the functor R one dimension down (a hypothesis here) identifies the two values on
the trace, and the push-forward and the deletion of empty blow-ups are the same.
H⁺ does not see the deleted members: the member i of F' is the member e i of E, and
the ideal is the same.
The trace of E − E^{e i} at the member e k is the trace of F' − F'^i at k (both empty at
k = i; E^{e k} = F'^k otherwise).
The trace of E − E^{e i} at a member outside the range of e is empty.
The modified core is indifferent to empty boundary members (the counterpart, for boundary
members, of [Kol07, 32]; the analogue of BDan.coreFamOn_indifferentToEmptyMembers without the
first blow-up): the modified core at the
member e i of E is the modified core at the member i of F'; the same H⁺, the same
restricted ideal, the boundaries corresponding along e, and the functor R one dimension down
indifferent (hRi).
coreModOn_indifferentToEmptyMembers for the CompatibleFamily coreModFam.