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Software evolution is a fact of life. Over the past thirty years, researchers have proposed hypotheses on how software changes, and provided evidence that both supports and refutes these hypotheses. To paint a clearer image of the software evolution process, we performed an empirical study on long spans in the lifetime of seven open source projects. Our analysis covers 653 official releases, and a combined 69 years of evolution. We first tried to verify Lehman's laws of software evolution. Our findings indicate that several of these laws are confirmed, while the rest can be either confirmed or infirmed depending on the laws' operational definitions. Second, we analyze the growth rate for projects' development and maintenance branches, and the distribution of software changes. We find similarities in the evolution patterns of the programs we studied, which brings us closer to constructing rigorous models for software evolution.