Because I do my algebra by hand, I hard-code it into my programs, and then it takes me a long time to adjust later. Let Mathematica take care of the algebra. Mathematica is an interpreted, interactive system in which, on a fundamental level, all of its operations share the same basic infrastructure. Flexibility from the shared infrastructure This shared infrastructure gives the user a level of flexibility that's unmatched in, frankly, the entire world of software.
Examples Let's define a simple function and also another function that uses the first one.
Let's try it out.