reserve ADG for Uniquely_Two_Divisible_Group;
reserve a,b,c,d,a9,b9,c9,p,q for Element of ADG;
reserve x,y for set;

theorem Th14:
  a,b ==> c,d implies a,c ==> b,d
proof
  assume a,b ==> c,d;
  then a + d = b + c by Th5;
  hence thesis by Th5;
end;
