We keep PROOF for those who still need it for legacy use cases. PROOF is not developed anymore and receiving only limited support. ROOT has since a few years moved to RDataFrame and related products as multi-core/multi-processing engines.
This function is unnecessary if the template parameter is RooAbsRealLValue (+ derived types) or RooAbsCategoryLValue (+derived types), as arg() will always return the correct type.
Use of TGeoTrack is deprecated. For the event display please switch to TEve (using TEveTracks or TEvePointSet to display tracks specifically) or to REve.