“…Clearly, one could restrict the solutions to be such that starting and ending slots need to be identical, that is, φ i = φ k . Although this would make the problem easy (see Section 3), it has been illustrated that this might lead to suboptimal solutions, i.e., solutions with a larger than necessary fuel cost [2]. Let us consider a triple (i, j, k) and the associated cost c(i, j, k).…”