"Nā kiam ta nā" pán-pún chi-kan bô-kāng--ê tē-hng

'''Nā chhiá ta nā''' ([[Eng-gí]]: ''if and only if''; '''iff''') sī chi̍t khoán [[lô-chek]] tiâu-kiāⁿ, khah chheng-chhó lâi kóng tiō sī '''nā-sī kiam ta-ū nā-sī''', sī piau-chún bu̍t-chit tiâu-kiāⁿ (''material conditional'') "ta nā" (tùi-tâng "nā ... tiō") kap i-ê tó-hoán "nā" cho͘-ha̍p--khí-lâi tùi nn̄g hāng tîn-su̍t ê [[siang-tiâu-kiāⁿ lô-chek|siang-tiâu-kiāⁿ]] [[lô-chek liân-chiap]] (''biconditional logical connective'') koan-hē.

 

 

Chit-ê tiâu-kiāⁿ kap [[pì-iàu kiam chhiong-chiok]] tiâu-kiāⁿ sī sio-siâng ê ì-sù. Nā kóng ''P nā chhiá ta nā Q'', ì-sù kap ''Q tùi P pì-iàu kiam chhiong-chiok'' sī sio-kâng--ê; mā kap ''P sī kap Q téng-ta̍t'' (''equivalent'') kâng ì-bī.