Axiom is sort of like Scratchpad source code converted to Literate Programming, and since TeX is near impossible to build these days, that makes Axiom score low on the hackability scale. Fricas on the other hand is much easier to build. However a lot of the equations that are programmed into the system, are sort of like ASCII art mathematics that the system is trained to decipher. A lot of those certainly got handed down over the decades of people figuring things out at IBM.