The obtaining of that advantage must have been the main or one of the main reasons for including or structuring the arrangements in the manner that resulted in the advantage.
Mae'n rhaid bod cael y fantais honno wedi bod yn brif reswm neu’n un o'r prif resymau dros gynnwys neu strwythuro'r trefniadau yn y modd a arweiniodd at y fantais.