public int setNeighbourNull(TetrahedronElt3D element, ScalarOperator sop) {
		
		TetrahedronElt3D neighbour = this.getNeighbour(0);
		if (neighbour != null && neighbour.isGeometryEquivalent(element, sop)) {
			this.eltZero = null;
			return 0;
		}
		neighbour = this.getNeighbour(1);
		if (neighbour != null && neighbour.isGeometryEquivalent(element, sop)) {
			this.eltOne = null;
			return 1;
		}
		neighbour = this.getNeighbour(2);
		if (neighbour != null && neighbour.isGeometryEquivalent(element, sop)) {
			this.eltTwo = null;
			return 2;
		}
		neighbour = this.getNeighbour(3);
		if (neighbour != null && neighbour.isGeometryEquivalent(element, sop)) {
			this.eltThree = null;
			return 3;
		}
		return -1;
	}