A Flowshop Scheduling Problem Related with Waiting-Times

We discuss a makespan problem of two machine flowshop in which any job waiting-time caus s a linear extension in the job processing-time on the second machine.The problem is known to he NP-hard when the waiting-time extension coefficients have two arbitrary values.In this paper, the problem is proved to be NP-hard too when the waiting-time extension coefficients have the same arbitrary value.