         return migrations.map { $0.identifier }.filter { appliedIdentifiers.contains($0) }
     }
     
-    /// Returns the identifiers of completed migrations, of which all previous
-    /// migrations have been applied.
-    ///
-    /// - parameter db: A database connection.
-    /// - throws: An eventual database error.
-    public func completedMigrations(_ db: Database) throws -> [String] {
-        let appliedIdentifiers = try appliedMigrations(db)
-        let knownIdentifiers = migrations.map(\.identifier)
-        return Array(zip(appliedIdentifiers, knownIdentifiers)
-            .prefix(while: { $0 == $1 })
-            .map { $0.0 })
-    }
-    
-    /// Returns true if all migrations are applied.
-    ///
-    /// - parameter db: A database connection.
-    /// - throws: An eventual database error.
-    public func hasCompletedMigrations(_ db: Database) throws -> Bool {
-        try completedMigrations(db).last == migrations.last?.identifier
-    }
-    
-    /// Returns whether database contains unknown migration
-    /// identifiers, which is likely the sign that the database
-    /// has migrated further than the migrator itself supports.
-    ///
-    /// - parameter db: A database connection.
-    /// - throws: An eventual database error.
-    public func hasBeenSuperseded(_ db: Database) throws -> Bool {
-        let appliedIdentifiers = try self.appliedIdentifiers(db)
-        let knownIdentifiers = migrations.map(\.identifier)
-        return appliedIdentifiers.contains { !knownIdentifiers.contains($0) }
-    }
-    
-    // MARK: - Non public
-    
-    private mutating func registerMigration(_ migration: Migration) {
-        GRDBPrecondition(
-            !migrations.map({ $0.identifier }).contains(migration.identifier),
-            "already registered migration: \(String(reflecting: migration.identifier))")
-        migrations.append(migration)
-    }
-    
-    /// Returns the applied migration identifiers, even unregistered ones
+    /// Returns the applied migration identifiers, even unregistered ones.
+    ///
+    /// See also `appliedMigrations(_:)`.
     ///
     /// - parameter db: A database connection.
     /// - throws: An eventual database error.

        }
    }
    
    /// Returns unapplied migration identifier,
    private func unappliedMigrations(upTo targetIdentifier: String, appliedIdentifiers: [String]) -> [Migration] {
        var expectedMigrations: [Migration] = []

    
    // MARK: - Querying Migrations
    
    /// Returns the identifiers of registered and applied migrations, in the
    /// order of registration.
    ///
    /// See also `appliedIdentifiers(_:)`.
    ///
    /// - parameter db: A database connection.
    /// - throws: An eventual database error.
