internal override TOutput Accept <TInput, TOutput>(
     CellTreeNode.SimpleCellTreeVisitor <TInput, TOutput> visitor,
     TInput param)
 {
     return(visitor.VisitLeaf(this, param));
 }
 internal abstract TOutput Accept <TInput, TOutput>(
     CellTreeNode.SimpleCellTreeVisitor <TInput, TOutput> visitor,
     TInput param);