internal override void VisitRefs(RefSet refSet, Action<CellRef> refAct, Action<CellArea> areaAct) { }
// Apply refAct once to each CellRef in expression, and areaAct once to each CellArea internal abstract void VisitRefs(RefSet refSet, Action<CellRef> refAct, Action<CellArea> areaAct);
internal override void VisitRefs(RefSet refSet, Action<CellRef> refAct, Action<CellArea> areaAct) {
foreach (Expr e in es) {
e.VisitRefs(refSet, refAct, areaAct);
}
}