function dy = repress(t,y,p)
 
   dy = zeros(6,1);
   dy(1) = -y(1) + p(1)/(1.+y(6)^p(4))+ p(2);
   dy(2) = -y(2) + p(1)/(1.+y(4)^p(4))+ p(2);
   dy(3) = -y(3) + p(1)/(1.+y(5)^p(4))+ p(2);
   dy(4) = -p(3)*(y(4)-y(1));
   dy(5) = -p(3)*(y(5)-y(2));
   dy(6) = -p(3)*(y(6)-y(3));