fix bug in contains check

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
fix bug in contains check

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
streamline condition, fix bugs in doc::subtract

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
fix bugs in doc

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