I AM having difficulty knowing what today's debate is about.

The difficulty for consumers is knowing which, if any, changes to make in what they buy.

The the difficulty is knowing what is going to be useful in the future.

Their ecological difficulties all knew about, though few understood their severity.

Now they say that they are eager to contact the world again, and that their difficulty is knowing how to begin.

The biggest difficulty is not knowing who you are going to play.

"The difficulty is knowing what the right thing is."

One difficulty is knowing how much precipitation might have fallen had any particular cloud not been seeded.

"The difficulty is knowing how long it would take to deliver those savings."

Some of the inverts are quite common, the employees at the printing plant presumably also having difficulties knowing which way was up.