>(depth-first 'newark 'san-francisco)
Extending the path (newark)
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Final path length is 18

Proceed from newark to indianapolis
then from indianapolis to chicago-midway
then from chicago-midway to bwi
then from bwi to las-vegas
then from las-vegas to san-diego
then from san-diego to los-angeles
then from los-angeles to denver
then from denver to chicago-ohare
then from chicago-ohare to charlotte
then from charlotte to ft-lauderdale
then from ft-lauderdale to dallas-ftworth
then from dallas-ftworth to honolulu
then from honolulu to bangkok
then from bangkok to hong-kong
then from hong-kong to beijing
then from beijing to tokyo
then from tokyo to san-francisco.
((san-francisco
   tokyo
   beijing
   hong-kong
   bangkok
   honolulu
   dallas-ftworth
   ft-lauderdale
   charlotte
   chicago-ohare
   denver
   los-angeles
   san-diego
   las-vegas
   bwi
   chicago-midway
   indianapolis
   newark))