mistake of law(Black's Law Dictionary - A mistake about the legal effect of a known fact or situation. - Also termed error in law; error of law. алешаBG)
unessential mistake(Black's Law Dictionary - A mistake that does not relate to the nature of the contents of an agreement, but only to some external circumstance, so that the mistake has no effect on the validity of the agreement. - Also termed inessential mistake; nonessential mistake; collateral mistake. алешаBG)
