2 ds020.hs:5: Pattern match(es) are overlapped in the definition of function `a':
3 a ~(~[], ~[], ~[]) = ...
5 ds020.hs:8: Pattern match(es) are overlapped in the definition of function `b':
6 b ~(~x : (~xs : ~ys)) = ...
8 ds020.hs:13: Pattern match(es) are overlapped in the definition of function `d':
12 ds020.hs:19: Pattern match(es) are overlapped in the definition of function `f':