ds020.hs:5: 
    Pattern match(es) are overlapped in the definition of function `a'
	    ~(~[], ~[], ~[]) = ...
ds020.hs:8: 
    Pattern match(es) are overlapped in the definition of function `b'
	    ~(~x : (~xs : ~ys)) = ...
ds020.hs:13: 
    Pattern match(es) are overlapped in the definition of function `d'
	    ~(n+43) = ...
	    ~(n+999) = ...
ds020.hs:19: 
    Pattern match(es) are overlapped in the definition of function `f'
	    (x@~[]) = ...


NOTE: Simplifier still going after 4 iterations; bailing out.