But I also realized there was more to my interest in his problems than a mental exercise.

I didn't come up with any answers, but it was good mental exercise.

Her mind again went through the mental exercises she'd learned as a child.

He enjoyed these mental exercises, and was good at them.

I was just running through mental exercises to hear myself think.

He looked at his watch, willing the sun to go down, and worked some mental exercises.

Not so good, maybe you need some more mental exercise.

At this point it was merely a mental exercise, but that would soon change.

Brown asserts playing the game is a form of mental exercise.