  Standard belief change assumes an underlying logic containing full classical
propositional logic. However, there are good reasons for considering belief
change in less expressive logics as well. In this paper we build on recent
investigations by Delgrande on contraction for Horn logic. We show that the
standard basic form of contraction, partial meet, is too strong in the Horn
case. This result stands in contrast to Delgrande's conjecture that orderly
maxichoice is the appropriate form of contraction for Horn logic. We then
define a more appropriate notion of basic contraction for the Horn case,
influenced by the convexity property holding for full propositional logic and
which we refer to as infra contraction. The main contribution of this work is a
result which shows that the construction method for Horn contraction for belief
sets based on our infra remainder sets corresponds exactly to Hansson's
classical kernel contraction for belief sets, when restricted to Horn logic.
This result is obtained via a detour through contraction for belief bases. We
prove that kernel contraction for belief bases produces precisely the same
results as the belief base version of infra contraction. The use of belief
bases to obtain this result provides evidence for the conjecture that Horn
belief change is best viewed as a hybrid version of belief set change and
belief base change. One of the consequences of the link with base contraction
is the provision of a representation result for Horn contraction for belief
sets in which a version of the Core-retainment postulate features.
