The following circumstances existing at the seller relieve them of liability if they prevent the performance of the contract or make the performance unreasonable: labor disputes and all other circumstances beyond the control of the seller, such as fire, war, mobilization, or unforeseen military call-ups of a corresponding extent, requisition, seizure, foreign exchange restrictions, riots and unrest, lack of transportation, unless this lack was foreseeable by the seller, general scarcity of goods, as well as defects in deliveries or delivery delays on the part of the upstream suppliers attributable to one of the circumstances mentioned in this paragraph. Circumstances such as those mentioned that existed before the conclusion of the contract only have the effect of relieving liability if their influence on the performance of the contract at the time of contract conclusion was unforeseeable by the seller. It is the seller's responsibility, if they wish to rely on a reason for exemption from liability mentioned in this paragraph, to notify the buyer of this reason immediately in writing. Without prejudice to the provisions of these terms and conditions of sale and delivery in other respects, each of the contracting parties may withdraw from the contract by written notice to the other party if a circumstance mentioned in this paragraph prevents the performance of the contract for more than six months.