extend observers for batch commit
reformat some code
introduce batch propagation in some ops
batch commits for aggregation
batch commit for cross prod and cyclic trans closure
batch commit for difference view
batch commit for duplicate elem, equi joins, exists in same domain, insetion view, naive transitive closure, not exists in same domain
projection set retaining
batch commit for projection view
batch commit for recursion base (by sequentializing batch)
batch commit for recursion DRed (by sequentializing batch)
batch commit for selection
batch commit for symm diff
batch commit for 3-way join
batch commit for trans closure acyclic graph store
batch commit for unnest
batch commit for union
batch commit for union max
batch commit for transactional equi join
batch commit for more transactional operators