hard and fast

not to be broken or changed；fixed；strict严格的；非遵守不可的；不能变动的

It's a hard and fast rule；everyone must obey it．这是个严格的规则，大家都必须服从。

The traffic regulations must be observed in a hard and fast way；any negligence would cause an accident．交通规则必须严格遵守，任何疏忽都会造成事故。

The teacher said that there was a hard and fast rule against smoking in the school．老师说校方规定不准抽烟，任何人不允许违反这条规定。