C++ :

#include<bits/stdc++.h>
using namespace std;
int a;
int main()
{
	cout<<"abcdefghijklm\nnopqrstuvwxyz\nzyxwvutsrqpon\nmlkjihgfedcba";
	return 0;
}

Pascal :

var c:char;i:integer;
begin
   i:=0;
   for c:='a' to 'z' do
     begin
       write(c);
       i:=i+1;
       if i mod 13=0 then writeln;
     
     end;
for c:='z' downto 'a' do
     begin
       write(c);
       i:=i+1;
       if i mod 13=0 then writeln;
     
     end;
  
end.