Where a legal system would appear to require an impossible proof, the remedies are reversing the burden of proof, or giving additional rights to the individual facing the probatio diabolica.
The devil's proof is the logical dilemma that while evidence will prove the existence of something, the lack of evidence fails to disprove it.
[1] This connects with the idea that, while substantial evidence may prove the devil's existence, there is no evidence that denies the devil's existence; therefore, one cannot deny the devil's existence.
The patent-holder would normally have to show that the patented process had been improperly used; this is a probatio diabolica, since, on the face of it, the patent-holder cannot prove which process was actually used, which could render the patent useless.
This legal article about a Latin phrase is a stub.