Snack Chips agrees to supply The Cafe with all the corn chips that it requires for a year at an agreed upon price. A sudden and unexpected demand for ethanol results in a shortgage of corn, and the price of corn rises sharply. Snack Chips ask Cafe to pay a higher price for the chips. This request is
invalid as an unethical attempt to profit more
invalid under the preexisting duty rule
valid because consideration can always be changed
valid due to the unforeseen difficulty of the sudden price increase