I couldn't be in two places at once, and they may have crossed the frontier.

"The head of the police cannot state whether or not he has crossed the frontier."

We cannot afford to let him cross the frontier and reach the river.

But this is also the only art that cannot cross frontiers.

Whatever visa you have, crossing the frontier takes a lot of time.

But my mother was killed trying to cross the frontier.

The mail to France crossed the frontier the next day.

We'll move very quickly once we cross the frontier and strike without warning.

Concepts beyond the most primitive could not yet cross the frontier.

They had passed three military patrols since they'd crossed the frontier.