书上说 we also ignore short-term debt, such as notes payable, because it is part of the capital provided to the company and is not considerd an operating item.
you may get working capital investment as: WC_t-WC_t-1 excluding cash, cash equivalents, notes payable and current portion of long-term debt. Basically it is: delta(AR) + delta(Inv.) -delta(AP) - delta(accrued taxes&expenses), delta = @T- @(T-1)