List expressions can be parsed
Included set type signature
Lists are now sets in the compiler
Set difference and union
Revert "Revert switch to sets"

This reverts commit 33ca35189768feb2b7167423a04cee453d773956.
Revert "Lists are now sets in the compiler"

This reverts commit 6bc8c0ae843468222b008b8d81f86baabb9bd67e.
Revert "Included set type signature"

This reverts commit 5cc869a5fa83982a27566a3117f94a815842935a.
Created the IndexedList type, with correct join and diff operations