Of interest to topos theorists ... because it shows that supports need not split
(“(SS) fails”) even in a topos where
(SG) Subobjects of 1 Generate, and
(IC) “Internal Choice” holds (i.e., epimorphisms split locally).
In particular, epimorphisms need not actually split,
i.e., (AC) may fail, i.e., the implication
(AC) ⇒ (IC) & (SG) is not reversible.
[NB: in contrast, for Grothendieck topoi, each of the implications
(AC) ⇒ (IC) & (SG) ⇒ (B) & (SG) is reversible, as
are those in
(AC) ⇒ (B) & (SS) ⇒ (B) & (SG) , so counterexamples must be non-Grothendieck.]
The topos: locally finite sheaves over Heath’s V-space.
(Local finiteness ⇒ (IC); 0-dimensionality of the
base ⇒ (SG).)
Same topos serves as counterexample to the reversibility of
several other implications
among similar conjunctions of
topos-theoretic conditions. [For details, consult the 30-year-old work
mentioned at the outset.]