>>72
Infix appears natural and simple because that's what you've been thought in school. What is simpler (+ 1 2 3 4 5 6 7 8 9) or 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9?
As for 3*x**2 + 4*x + y + 4, (+ (* 3 x x) (* x 4) y 4) is pretty readable to me. It's only confusing the first few days/week of looking at it. It becomes as natural as infix after you've used it for a week or so, moreso if you use a structured editing package like Paredit.