ds020.hs:5: Pattern match(es) are overlapped in the definition of function `a':
	    a ~(~[], ~[], ~[]) = ...

ds020.hs:8: Pattern match(es) are overlapped in the definition of function `b':
	    b ~(~x : (~xs : ~ys)) = ...

ds020.hs:13: Pattern match(es) are overlapped in the definition of function `d':
	    d ~(n+43) = ...
	    d ~(n+999) = ...

ds020.hs:19: Pattern match(es) are overlapped in the definition of function `f':
	    f (x@~[]) = ...