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␈↓ ↓H␈↓␈↓βS␈↓∧ Artificial Intelligence Laboratory, STANFORD UNIVERSITY, Stanford, California 94305
␈↓ ↓H␈↓∧Telephone 415 497-4430␈↓ 	dDecember 3, 1975




␈↓ ↓H␈↓Martin Gardner
␈↓ ↓H␈↓Scienti≡c American
␈↓ ↓H␈↓415 Madison Avenue
␈↓ ↓H␈↓New York, New York 10017

␈↓ ↓H␈↓Dear Martin:

␈↓ ↓H␈↓        I␈αjust␈αremembered␈αanother␈α
geographical␈αquestion:␈αHow␈αmany␈α
states␈αmust␈αone␈αdrive␈α
through
␈↓ ↓H␈↓in␈αgoing␈αfrom␈αBoston␈αto␈αSan␈αFrancisco␈αstaying␈αwithin␈αthe␈αU.S.?␈α Curiously,␈αa␈αlook␈αat␈αa␈αmap␈αdoes
␈↓ ↓H␈↓not␈α⊂give␈α⊃the␈α⊂answer.␈α⊃ If␈α⊂one␈α⊂can␈α⊃drive␈α⊂from␈α⊃Kentucky␈α⊂to␈α⊂Missouri,␈α⊃then␈α⊂the␈α⊃answer␈α⊂is␈α⊃ten␈α⊂-
␈↓ ↓H␈↓otherwise␈αeleven.␈α But␈αthere␈αis␈αapparently␈αno␈αbridge␈αacross␈αthe␈αMississippi␈αdirectly␈α
between␈αthese
␈↓ ↓H␈↓states,␈αI␈αdon't␈αknow␈αabout␈αcar␈αferries,␈αnor␈αdo␈αI␈αknow␈αfor␈αsure␈αwhether␈αthe␈αbridge␈αat␈αCairo,␈αIllinois
␈↓ ↓H␈↓permits passage from Kentucky to Missouri without going through Illinois, but apparently not.


␈↓ ↓H␈↓Sincerely,



␈↓ ↓H␈↓John McCarthy
␈↓ ↓H␈↓Director
␈↓ ↓H␈↓Professor of Computer Science