  Canonical inference rules and canonical systems are defined in the framework
of non-strict single-conclusion sequent systems, in which the succeedents of
sequents can be empty. Important properties of this framework are investigated,
and a general non-deterministic Kripke-style semantics is provided. This
general semantics is then used to provide a constructive (and very natural),
sufficient and necessary coherence criterion for the validity of the strong
cut-elimination theorem in such a system. These results suggest new syntactic
and semantic characterizations of basic constructive connectives.
