6.0 macs:Mac OS X10.4.1 SntP 10 @x Cube(x) $ Small(x) ; This still has a free occurrence of x. Fix it with ; some parentheses. /a Cube(a) ; Don't forget that quantifiers apply only to ; variables. /v Cube(v) & Medium(v) & Larger(v, c) /u (Small(u) & Cube(u) ~/x Larger(a, x) & Larger(x, a) @w SameRow(w, b) $ SameRow(b, w) @x @y @z LeftOf(x, y) & LeftOf(y, z) $ LeftOf(x, z) @x @y (Larger(a, b) $ Cube(a) & Dodec(b)) ; This one is a bit tricky. The problem is some ; missing parentheses. @x @y Cube(x) & Cube(y) $ LeftOf(x, y) @x (Cube(x) $ /x Between(x, x, y)) s=91751;