public void addEquivalent(ExprAggregateNode aggNodeToAdd){
  if (equivalentNodes == null) {
    equivalentNodes=new ArrayList<ExprAggregateNode>();
  }
  equivalentNodes.add(aggNodeToAdd);
}

public void addEquivalent ( ExprAggregateNode aggNodeToAdd ) { if ( equivalentNodes == null ) { equivalentNodes = new ArrayList < ExprAggregateNode > ( ) ; } equivalentNodes . add ( aggNodeToAdd ) ; }
add an equivalent aggregation function node
