a. A schematic diagram of hedgehog regulation of tumor growth in the cerebellum is shown. These proteins are key components of the hedgehog signaling pathway, though many intermediate enzymes may mediate some steps. The "transforming event" is hypothesized to be required for tumor growth, but details about its function are completely lacking . Tumor growth is a macroscopically defined process that is connected to molecular dynamics using rules. b. The rules for this model are given in linguistic form, much as they might be described in journal articles that discuss this pathway.