The
doctrine of equivalents is a legal rule in most of the world's
patent systems that allows a
court to hold a party liable for
patent infringement even though the infringing device or process does not fall within the literal scope of a
patent claim, but nevertheless is equivalent to the claimed
invention. U.S. judge
Learned Hand has described its purpose as being "to temper unsparing logic and prevent an infringer from stealing the benefit of the invention".