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This paper discuses the case of Bruckelmyer v. Ground Heaters, Inc which involved a problem unique to the construction industry in colder climates. In order to harden properly, concrete must be kept from freezing before it sets up. Mr. Bruckelmyer knew about this problem and came up with a system for prethawing large areas of frozen ground so that concrete could be poured all winter all. His solution was to lay out a serpentine pattern of hoses over the frozen ground and then pass hot water or antifreeze through the hoses to heat the ground below. The hoses were covered with a thermal blanket so that thawing rates of a foot per day could be achieved. Bruckelmyer obtained two U.S. patents and proceeded to sign up licensees to practice his invention. One of those licensees, Ground Heaters, Inc., subsequently canceled its license but kept on practicing the technology. Bruckelmyer responded by bringing suit for patent infringement. As Ground Heaters looked for prior art to knock out Bruckelmyer's patents, it found an old Canadian patent that showed the use of hot water hoses to heat concrete forms but not to heat the ground. In the Canadian file were two additional figures that had been included in the original application but were canceled during prosecution and those not part of the issued patent. Those figures showed using a hose system to thaw frozen ground, exactly what Bruckelmyer has patented. CAFC struggle with the issue and in the end ruled in Ground Heater's favor and found that the two old Canadian drawings were prior art and thus Brucklmyer's patent was invalid.