anchor.diff:  
       M1 = M0#{1=>42,2=>100,4=>[a,b,c]},
       #{1:=42,2:=100,3.0:=c,4:=[a,b,c],5:=e} = M1,
  -    M1 = M0#{1.0=>wrong,1:=42,2.0=>wrong,2.0=>100,4.0=>[a,b,c]},
  +    #{1:=42,2:=b,4:=d,5:=e,2.0:=100,3.0:=c,4.0:=[a,b,c]} = M0#{1.0=>float,1:=42,2.0=>wrong,2.0=>100,4.0=>[a,b,c]},
   
       M2 = M0#{3.0=>new},
       #{1:=a,2:=b,3.0:=new,4:=d,5:=e} = M2,
  
positive.code:     {ok, 1}     = maps:find(a, #{ a=> 1}),
      {ok, 2}     = maps:find(b, #{ a=> 1, b => 2}),
      {ok, "int"} = maps:find(1, #{ 1   => "int"}),
      {ok, "int"} = maps:find(1.0, #{ 1 => "int"}),
      {ok, "float"} = maps:find(1, #{ 1.0  => "float"}),
      {ok, "float"} = maps:find(1.0, #{ 1.0=> "float"}),
  
      {ok, "hi"} = maps:find("hello", #{ a=>1, "hello" => "hi"}),
      {ok, "tuple hi"} = maps:find({1.0,1}, #{ a=>a, {1,1.0} => "tuple hi"}), % reverse types in tuple key
  
      M = id(#{ k1=>"v1", <<"k2">> => <<"v3">> }),
      {ok, "v4"} = maps:find(<<"k2">>, M#{ <<"k2">> => "v4" }),
  
negative.code:     %% error case
      error = maps:find(a,#{}),
      error = maps:find(a,#{b=>1, c=>2}),
      error = maps:find(1.0, #{ 1 => "int"}),
      error = maps:find(1, #{ 1.0  => "float"}),
      error = maps:find({1.0,1}, #{ a=>a, {1,1.0} => "tuple hi"}), % reverse types in tuple key
  
  
      {'EXIT',{badarg,[{maps,find,_,_}|_]}} = (catch maps:find(a,[])),
      {'EXIT',{badarg,[{maps,find,_,_}|_]}} = (catch maps:find(a,<<>>)),
  