How the relations were inferred
Containment. A crater lying entirely inside another crater's rim must be younger: the larger impact would have erased anything inside its rim.
Rim overlap. Where two rims cross, the younger rim stays intact. Robbins's rim tracing (the traced fraction of each rim in THEMIS imagery) and a rim-continuity test on MOLA topography each say which rim is missing where the other crater sits; edges are kept when the rim-arc test decides, alone or agreeing with topography.
Checks. Rim-arc and topography calls agree 98% of the time; oriented edges match Robbins degradation states as often as the geometrically certain containment edges do; in a blind visual check on CTX images, the order matched for 38 of the 40 judgeable pairs whose edges appear here.
Arrows show the transitive reduction: an implied relation (A before C, given A before B before C) is not drawn.