Parameter variables
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## Parameter variables

As we said before, there exist special variables called parameters that exist in all scopes. To declare a parameter called `foo` with the initial value 1, we write

    parameter foo = 1

From then on, `foo` is a strictly global variable. Setting `foo` inside any function will modify the variable in all contexts, that is, functions do not have a private copy of parameters.

When you undefine a parameter using the `undefine` function, it stops being a parameter.

Some parameters are built-in and modify the behavior of genius.

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