However, it is impossible to ensure complete containment for all time.
Without proper maintenance of the railway track it is impossible to ensure sustainable railway superstructure.
And once something is online, it is virtually impossible to ensure that all copies are deleted.
In 2008, eBay banned the sale of ivory, finding it impossible to ensure trade was legal.
"It is impossible to ensure safety sufficiently to prevent the risk of a national collapse," Mr. Kan said.
"It's very expensive to monitor this hunt, and it's impossible to ensure a humane death in conditions like these.
Without transparency about lethal injections, particularly the source and purity of drugs to be used, it is impossible to ensure that executions are humane and constitutional.
But Professor Dill says the inherent complexity of software code makes it nearly impossible to ensure that computerized elections are fair.
They also worried that a permanent test ban might make it impossible to ensure that warheads in America's nuclear stockpile had not deteriorated.
Officials of the development corporation said it would be impossible to ensure construction on higher platforms after the museum was built.
Mr. Gould says it is impossible to ensure that all retailers take the next step: encrypting the numbers again, according to rules set by the card networks.
