S9fES  (trace symbol ...)  ==>  list | #t
       (trace #t)          ==>  list | #t
       (trace)             ==>  list | #t

Trace the procedures or syntax objects bound to the given
symbols. When #T is passed to trace, trace all procedures
and syntax objects (expect lots of output!). When no arguments
are passed to it, disable tracing. TRACE returns the symbols
that were being traced before its invocation.

(trace 'foo)       ==>  ()
(trace 'bar 'baz)  ==>  (foo)
(trace #t)         ==>  (bar baz foo)
(trace)            ==>  #t
