Use constructor methods for RelOptRuleOperand: RelOptRule.leaf(), .some(), .any();
use "call.rel(x)" rather than "(Cast) call.rels[x]";
remove @author, @version, @since tags.
Revert to snapshot version number.
MongoDB adapter: Push down projects.
Add some methods to Pair, and rename some.
Add "enabled(boolean)" method to OptiqAssert.