《世说新语·文学》
他随便地谈到《四本论》，便像汤他铁城，使人找不到可以进攻的机会。
忽言及四本，便苦汤池铁城，无可攻之势。
Whenever he casually discussed the Theory of the Four Roots, he resembled a fortress made of iron and clay, giving his opponents no opportunity to attack.