////////////////////////
nei:=function(C,x);
   n:=Length(C);
   D:=C meet Dual(LinearCode<GF(2),n|x>);
   G:=GeneratorMatrix(C);
   for i in [1..Dimension(C)] do;
     if (G[i],x) eq 1 then;
       y:=G[i];
     break i;
     end if;
   end for;
   N1:=[LinearCode<GF(2),Length(D)|D,z>:z in [x,x+y]];
return N1;
end function;
////////////////////////

// Example
C:=ExtendCode(QRCode(GF(2),23));
x:=Vector(GF(2),24,[1,1] cat [0: i in [1..22]]);
nei(C,x);