 When a disease is over, for many diseases there are over, some as you know are not, it's as simple as, I'll go back to COVID, you know, people would take a COVID test when they felt better to say, I no longer have enough of the virus present to be infectious, to be able to transmit. So that's one aspect, but that's a simple one. What we've learned with cancer is we have a new test called MRD, minimal residual disease.