5課 関連・無関係 教科書 p.24〜27
Regarding / regardless of — depending on…, despite…, in spite of…
接続：名／普通形 ＋ ならいざしらず
If it's... then it's okay, over here.... Compare: that case is acceptable, but this case is not.
注意 / Note：The latter part is often the speaker's dissatisfaction, surprise, and criticism.
比較 / Compare：〜ならいざしらず ≒ 〜ならまだしも（補足）; The latter are all discontent/surprise.
よく出る形 / Common form：名／普通形＋ならいざしらず＋（不満・驚きの文）.
安いホテルならいざしらず、一流ホテルでこのサービスは許せない。
A cheap hotel is fine, but a luxury hotel with service like this is unacceptable.
5歳の子供ならいざしらず、大人がこんなことを知らないなんておかしい。
It's okay for a 5 year old child, it's strange for adults not to know this.
初心者ならいざしらず、経験者がこんな失敗をするとは。
It's okay for a newbie, but it's a shame if an experienced person makes this mistake.