Simply Logical (free book)

It's a free ebook about Prolog. I started reading it some time ago, and looked very promising, with a balanced combination between theory and practice.

But, as with any other book about Prolog I've tried to read I hit a wall, and got stuck. Maybe I'm too dumb to grasp it, or just don't have enough time. I took some classes in college, and remember that never really "got it", just the enough pass the exams. I have tried to overcome that a couple times since then but it's harder when you have a job and a family.