being pedantic about not too much

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
use flat conjunctions/disjunctions instead of iterative

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
fixing 0-arity case for unreachable nodes, leaving reachable nodes as exercise :-)

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>