The following group of function enable or disable tracing of specific stages of the unification process:
(trace-determine :on t|nil)
(trace-category :all|cat|(cat1...catn) t|nil)
(trace-bk-class t|nil)
(trace-wait :on t|nil)
(trace-cset :on t|nil)
(trace-alts :on t|nil)
(hyper-trace-category cat :status t|nil)
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