We prove the weak-strong uniqueness for measure-valued solutions
of the incompressible Euler equations. These were introduced by R.DiPerna
and A.Majda in their landmark paper , where in particular global existence
to any L2 initial data was proven. Whether measure-valued solutions agree
with classical solutions if the latter exist has apparently remained open.
We also show that DiPerna's measure-valued solutions to systems of con-
servation laws have the weak-strong uniqueness property.