sort . sort = sort
+++ Tests passed.

length . nub = length  (incorrect when there are repeated elements)
*** Falsified, counterexample:  [0,0]
               generalization:  x:x:xs

xs `union` ys == ys `union` xs  (incorrect for repeated elements)
*** Falsified, counterexample:  ([],[0,0])
               generalization:  (xs,x:x:xs)
               generalization:  ([],x:x:xs)

\(x,y) -> x + y == y + x
+++ Tests passed.

\x -> x == x + 1  (always incorrect)
*** Falsified, counterexample:  0
               generalization:  x

\(x,y) -> x + y == x + x  (incorrect)
*** Falsified, counterexample:  (0,1)

\(x,y) -> x /= y  (incorrect whenever x and y are equal)
*** Falsified, counterexample:  (0,0)
               generalization:  (x,x)