Function restore 

pub fn restore(fam: DerivedFamily, exp: &ExpandedFamily) -> DerivedFamily

Restore a raw expanded-family derivation (S3): rewrite the auxiliary type-formers / constructors back to the real container in every recursor type and rule, re-key rules by the real constructor, drop the auxiliary inductives and constructors, keep only the original types’ inductives and constructors (with num_nested set and all narrowed to the originals), and RETAIN the auxiliary recursors — now stated over the real container — because reducing a user-facing recursor still emits them.