ntById("button_" + n);
    radio_n.disabled = true;
}

///////
/// solver 2
var solver_2_eq_1_temp;
var solver_2_eq_2_temp;
function set_solver_2() {
    solver_2_eq_2_temp = solver_1_eq_2;
    solver_2_eq_1_temp = solver_1_eq_1;  
}

function invalidate_solver_2(client_x, client_y) {
    var solver = document.getElementById("solver_2");
    var canvas_rect = solver.getBoundingClientRect();
    if(document.getElementById("button_1").disabled){
           eval("solver_1_eq_" + solver_1_eq_temp_id + " = Array