There was something in her manner that made me think I'd best provide concrete proof of my identity.

The hard part is that neither of us has any concrete proof.

They want concrete proof that the child has learned useful skills.

But the talks produced no concrete proof of any change in doctrine.

I'm not absolutely certain and I don't have any concrete proof.

"There is no concrete proof of anything that he directly had his hand in."

The problem was, there really wasn't any concrete proof of death.

But the judge did not find concrete proof of wrongdoing.

Early in the ride we received concrete proof of how desperate was the situation.

Not just belief there is concrete proof of their success.