pred := preds[i]
			if blockLocs[pred.ID].lastChangedTime > locs.lastCheckedTime {
				continue // keep this predecessor
			}
			preds[i] = preds[len(preds)-1]
			preds = preds[:len(preds)-1]
			if state.loggingLevel > 2 {
				state.logf("Pruned b%d, lastChanged was %d but b%d lastChecked is %d\n", pred.ID, blockLocs[pred.ID].lastChangedTime, b.ID, locs.lastCheckedTime)
			}
		}