Combine multiple “from” relations into a single CrossRelation.
Combine multiple “from” relations into a single CrossRelation.

This eliminates some duplication where we define an operation on a CrossRelation and then effectively fold the same operation over the top-level list. It also simplifies some cases where we “knew” the list was non-empty and can now show that in the types.

mossprescott/quasar,djspiewak/quasar,jedesah/Quasar,jedesah/Quasar,wemrysi/quasar,drostron/quasar,quasar-analytics/quasar,slamdata/slamengine,drostron/quasar,slamdata/slamengine,drostron/quasar,jedesah/Quasar,mossprescott/slamengine,jedesah/Quasar,slamdata/quasar,slamdata/slamengine,quasar-analytics/quasar,drostron/quasar,mossprescott/quasar,quasar-analytics/quasar,wemrysi/quasar,quasar-analytics/quasar,mossprescott/slamengine