started definition of logic tree elements
started definition of logic tree elements


Former-commit-id: 7c6672342f63043830d6dbf196f1b88c4b4a426c [formerly 0bd531cb9c7fc6bee1665618094182d8c0343743]
Former-commit-id: 5beba8d9332a37db199a456e789674e9946eda11
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine