He agreed to their visit with the proviso that they should stay no longer than one week.
他同意他们来做客，但条件是逗留不得超过一周。
《牛津词典》
2
So overall (and with the huge proviso that you do not count the fossil fuel used to farm the stuff) biofuels are carbon-neutral.
因此，总体来讲，生物燃料是属于碳中性的，但条件是人们不会去计算制造生物燃料所要耗费的化石燃料。
3
With the centralisers, an earlier decision—to run only one pipe down the well, making it easier for gas and oil to get up—had been taken with the proviso that extra care would be needed in cementing.