ERROR: cannot find the numeric property 'special_property_name' for device: instance_name [model_name], required for perc::

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    Unlike LVS, PERC does not perform device reduction by default.  When XFORM REDUCTION is specified, PERC will perform device reduction.  You need to write an effective property computation routine (in an LVS Reduce statement) if you want to reduce device properties that are not built-in.