public Code[] FilterStuff(
        DateTime departureDate,
        Code[] codes,
        Partner partner
    ) =>
        _hotels
            .TryFind(partner)
            .Map<
                FrozenDictionary<Code, Entry>,
                Code[],
                (Code[] codes, DateTime date)
            >(
                static (entries, ctx) =>
                    [
                        .. ctx.codes.Where(code =>
                            hotels
                                .TryFind(code)
                                .Map(
                                    static (entry, date) =>
                                        entry.ValidityPeriods.Any(period =>
                                            period.From <= date
                                            && period.To >= date
                                        ),
                                    ctx.date
                                )
                                .Or(() => false)
                                .Value
                        ),
                    ],
                (codes, date)
            )
            .Or(() => [])
            .Value;

    public Code[] FilterStuff(
        DateTime departureDate,
        Code[] codes,
        Partner partner
    ) =>
        _hotels
            .TryFind(partner)
            .Map<
                FrozenDictionary<Code, Entry>,
                Code[],
                (Code[] codes, DateTime date)
            >(
                static (entries, ctx) =>

                    [
                        .. ctx.codes.Where(code =>
                            hotels
                                .TryFind(code)
                                .Map(
                                    static (entry, date) =>
                                        entry.ValidityPeriods.Any(period =>
                                            period.From <= date
                                            && period.To >= date
                                        ),
                                    ctx.date
                                )
                                .Or(() => false)
                                .Value
                        ),
                    ],
                (codes, date)
            )
            .Or(() => [])
            .Value;

                static (entries, ctx) =>
// EMPTY LINE
                    [