“…This question, along with the closely related problems of determining the minimum number of subtree prune and regraft, respectively tree bisection and reconnection, operations required to transform one phylogenetic tree into another (the rSPR Distance and TBR Distance problem, respectively) has been considered in a number of papers [1,2,3,5,10,12,17,18]. Key theoretical developments have shown that each of these three problems is NPhard even in the restricted case that the input consists of two binary phylogenetic trees [4,6,12], but also that they are all fixed-parameter tractable in their respective natural parameters [1,4,5].…”