Now consider the case of a chain of two decays: one nuclide decaying into another by one process, then decaying into another by a second process, i.e. "". The previous equation cannot be applied to the decay chain, but can be generalized as follows. Since decays into , "then" decays into , the activity of adds to the total number of nuclides in the present sample, "before" those nuclides decay and reduce the number of nuclides leading to the later sample. In other words, the number of second generation nuclei increases as a result of the first generation nuclei decay of , and decreases as a result of its own decay into the third generation nuclei . The sum of these two terms gives the law for a decay chain for two nuclides: