public void setSubExpressions(int i, Expression expr) {
		int diff = expr.getFreeOperandCount()
				- subExpressions[i].getFreeOperandCount();
		subExpressions[i] = expr;
		expr.parent = this;
		for (Operator ce = this; ce != null; ce = (Operator) ce.parent)
			ce.operandcount += diff;
		updateType();
	}