x_{1} is a logical statement which says that x_{2} (du'u) being true logically implies (material implication) x_{3} being necessarily true, but in which the converse does not hold (it is certain that there are cases in which 'IFF' fails: x_{2} is not necessary for x_{3}).

Strict-'IF'; the truth of x_{2} guarantees the truth of x_{3} but the truth of x_{3} gives no indication about the truth of x_{2} (in general). This word is like kanxe. See also: 3 is true if x_{2} is true; if x_{2}, then x_{3}; x_{2} being true is sufficient to guarantee the truth of x_{3}").">sigda.