function change(){
                                    document.getElementById("home").style.visibility = "hidden";
                                    document.getElementById("home2").style.visibility = "visible";
                                   }
                  function back() {
                                    document.getElementById("home").style.visibility = "visible";
                                    document.getElementById("home2").style.visibility = "hidden";
                                   }

                  function change2(){
                                    document.getElementById("eng1").style.visibility = "hidden";
                                    document.getElementById("eng2").style.visibility = "visible";
                                   }
                  function back2() {
                                    document.getElementById("eng1").style.visibility = "visible";
                                    document.getElementById("eng2").style.visibility = "hidden";
                                   }
                  function change3(){
                                    document.getElementById("contact1").style.visibility = "hidden";
                                    document.getElementById("contact2").style.visibility = "visible";
                                   }
                  function back3() {
                                    document.getElementById("contact1").style.visibility = "visible";
                                    document.getElementById("contact2").style.visibility = "hidden";
                                   }

                  function change4(){
                                    document.getElementById("contact3").style.visibility = "hidden";
                                    document.getElementById("contact4").style.visibility = "visible";
                                   }
                  function back4() {
                                    document.getElementById("contact3").style.visibility = "visible";
                                    document.getElementById("contact4").style.visibility = "hidden";
                                   }