ds020.hs:9:1: warning: [-Woverlapping-patterns (in -Wdefault)]
    Pattern match is redundant
    In an equation for ‘a’: a ~(~[], ~[], ~[]) = ...

ds020.hs:12:1: warning: [-Woverlapping-patterns (in -Wdefault)]
    Pattern match is redundant
    In an equation for ‘b’: b ~(~x : ~xs : ~ys) = ...

ds020.hs:19:1: warning: [-Woverlapping-patterns (in -Wdefault)]
    Pattern match is redundant
    In an equation for ‘d’: d ~(n+43) = ...

ds020.hs:20:1: warning: [-Woverlapping-patterns (in -Wdefault)]
    Pattern match is redundant
    In an equation for ‘d’: d ~(n+999) = ...

ds020.hs:23:1: warning: [-Woverlapping-patterns (in -Wdefault)]
    Pattern match is redundant
    In an equation for ‘f’: f x@(~[]) = ...