(defined? name), where name is a symbol, returns #t if a global variable is defined with the name name, or #f otherwise.
(undefine name), where name is a symbol, causes name to be undefined if it was defined previously.
(global-define-value name) returns the value of the global variable named by the symbol name. If name is undefined, the exn:variable exception is raised.
(make-global-value-list) returns an association list that pairs each globally-defined symbol with its current value.