Frame、environment、binding 這些東西的定義就在前一章：
https://mitpress.mit.edu/sicp/full-text/sicp/book/node55.html
An environment is a sequence of frames. Each frame is a table
(possibly empty) of bindings, which associate variable names with
their corresponding values. (A single frame may contain at most
one binding for any variable.) Each frame also has a pointer to
its enclosing environment, unless, for the purposes of this
discussion, the frame is considered to be global. The value of a
variable with respect to an environment is the value given by the
binding of the variable in the first frame in the environment
that contains a binding for that variable. If no frame in the
sequence specifies a binding for the variable, then the variable
is said to be unbound in the environment.