function f=dreikoerper(t,y,mu)

mup = 1-mu;
f = zeros(4,1);

f(1) = y(3);
f(2) = y(4);

help1 = ((y(1)+mu)^2+y(2)^2)^(3/2);
help2 = ((y(1)-mup)^2+y(2)^2)^(3/2);

f(3) = y(1) + 2*y(4)-mup*(y(1)+mu)/help1-mu*(y(1)-mup)/help2;
f(4) = y(2)-2*y(3)-mup*y(2)/help1-mu*y(2)/help2;