mathlib

6a6b4d05 - feat(category_theory/sites/*): Cover-lifting functors on sites (#9431)

feat(category_theory/sites/*): Cover-lifting functors on sites (#9431) This PR defines cover-liftings functors between sites, and proves that `Ran F.op` maps sheaves to sheaves for cover-lifting functors `F`. This will probably be needed when we want to glue B-sheaves into sheaves. Co-authored-by: erdOne <36414270+erdOne@users.noreply.github.com>