Future work: SO predicates

[monadplus]

Proposal 1

1. Parse SO-CEL queries and split them in (a) CEL and (b) SO-CEL
   a. output should be processable by CORE i.e. unary predicates.
   b. output should encode the information needed to process first-order queries' output with second-order predicates.
2. Given (a) to CORE and execute update (phase 1)
3. On phase 2, use (b) to do, at the same time, the enumeration and the application of second-order predicates.
   3.1. Use dtECS enumeration algorithm and replace the mock of so predicates with an actual implementation that uses (b).