Could you elaborate on this a bit more? How could one gain anything from buying negative yielding bond?
So for example let's say you bought a -0.1% yield, but newly issued bonds are now only offering a -0.5% yield you can now actually sell your bonds paying out -0.1% at a profit, since even if they paid you a 3.5% premium on the price you paid, it would still be more attractive than the rate on offer for new bonds.