private Face(Tet tetLeft, Node nodeLeft, Tet tetRight, Node nodeRight) { if (tetLeft!=null) { initLeft(tetLeft,nodeLeft); } else if (tetRight!=null) { initRight(tetRight,nodeRight); } else { assert false:"either tetLeft or tetRight is not null"; } _tetLeft = tetLeft; _tetRight = tetRight; _nodeLeft = nodeLeft; _nodeRight = nodeRight; }