updates for mux
more optiq wip
working sort prule
Add Partition Trait. WIP.
Add partition Trait. More WIP.
Switch back to Mux trait.  Union-exchange on either single/multiple files.
Revert "Switch back to Mux trait.  Union-exchange on either single/multiple files."

This reverts commit 32ee1819e3dde9f2a98ef9124ade3c37e2e25641.
exchange rule. more wip.
Exchange rules: first set of rules that works using new trait.