Bing Yin (丙寅) and Ding Mao (丁卯) represent the "Fire in the Furnace." Yin (寅) corresponds to the third Yang, and Mao (卯) corresponds to the fourth Yang. The fire gains its foundation and is nourished by the wood of Yin (寅) and Mao (卯). At this time, heaven and earth open the furnace, and all things begin to be born, hence it is called "Fire in the Furnace."