## The Possibility of a Side-Register

The possibility can be considered, that in a certain implementation of LISP, a side-register on the CPU keeps track of what the data-type is, that the main register points to. But as the following experiment shows, this would only help accelerate how LISP expressions are evaluated, and does not affect how Common LISP in particular, stores the data-type in a variable. I.e., on the assumption that the data-type is held in a side-register, we could additionally assume that it gets inserted into the plist of a symbol, whenever we assign the value to the symbol. And what I have shown below, is that this additional assumption would be false, in the case of Common LISP: