'Print trace output displaying that ``production`` was used to
reduce ``stack``.
:rtype: None'

def _trace_reduce(self, stack, production, remaining_text):

    if (self._trace > 2):
        rhs = u'    '.join(production.rhs())
        print((u'Reduce    %r    <-    %s' % (production.lhs(), rhs)))
    if (self._trace == 2):
        self._trace_stack(stack, remaining_text, u'R')
    elif (self._trace > 1):
        self._trace_stack(stack, remaining_text)
