ds020.hs:8:1: Warning:
    Pattern match(es) are overlapped
    In an equation for ‘a’: a ~(~[], ~[], ~[]) = ...

ds020.hs:11:1: Warning:
    Pattern match(es) are overlapped
    In an equation for ‘b’: b ~(~x : ~xs : ~ys) = ...

ds020.hs:16:1: Warning:
    Pattern match(es) are overlapped
    In an equation for ‘d’:
        d ~(n+43) = ...
        d ~(n+999) = ...

ds020.hs:22:1: Warning:
    Pattern match(es) are overlapped
    In an equation for ‘f’: f x@(~[]) = ...