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(* Open Source License                                                       *)
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(** A [trace] is a stack of [error]s. It is implemented as an [error list]
    but such a list MUST NEVER be empty.

    It is implemented as a concrete [error list] for backwards compatibility
    but future improvements might modify the type or render the type
    abstract. *)
include Sig.TRACE with type 'err trace = 'err list