Multiple symbols per single line in a legend

Hello everybody,

Is it possible to coax legend() into displaying more than one simbol per
line in legend? I have a graph like the one attached to this mail; I would
like to reorganize the legend in such a way that the duplicate text would be
omitted, i.e., the first line would read <square> <triangledown> "increasing
frequency" and the second one would read <circle> <triangleup> "decreasing
frequency". Before resorting to box() and text() I would like to check
whether some clever method already exists that would solve my problem. :)

Thanks in advance.

All the best,
Primoz
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