The resistors prevent the (unlikely) occurrence of a short-circuit between two or more inverter gates, if one gate happens to fail high or low, or if some gates are significantly slower than others (and thus will fight with the faster gates during each transition).



Challenge question: adding inverter gates to the output of this circuit has an interesting effect on the duty cycle control. The potentiometer will now act backward from the way it was before (decreasing duty cycle when it formerly increased duty cycle, and visa-versa). Explain why.