private ArrayList<AlgebraicParticle> children(Algebra a) {
		if(a instanceof Equation) return list(((Equation)a).left(), ((Equation)a).right());
		if(a instanceof AlgebraicCollection) return ((AlgebraicCollection)a).toList();
		if(a instanceof Fraction) return list(((Fraction)a).getTop(), ((Fraction)a).getBottom());
		if(a instanceof MixedNumber) return list(((MixedNumber)a).getNumeral(), ((MixedNumber)a).getFraction());
		if(a instanceof Root) return list(((Root)a).getExpr());
		else return null;
	}