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




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

␈↓ ↓H␈↓Dear Martin:

␈↓ ↓H␈↓        Your␈αgeographical␈αquestions␈αremind␈αme␈αof␈α
a␈αhard␈αone␈αthat␈αI␈αaccidentally␈α
discovered␈αwhile
␈↓ ↓H␈↓looking␈αat␈αa␈αlarge␈αglobe.␈α Find␈αtwo␈αplaces␈αin␈αthe␈αworld␈αthat␈αused␈αto␈αhave␈αthe␈αsame␈αname␈αand␈αare
␈↓ ↓H␈↓diametrically␈αopposite␈αeach␈αother,␈αi.e.␈αyou␈αcan␈αgo␈αfrom␈αone␈αto␈αthe␈αother␈αby␈αgoing␈αstraight␈αthrough
␈↓ ↓H␈↓the␈αcenter␈αof␈αthe␈αearth.␈α The␈αpoles␈αdon't␈αcount.␈α The␈αanswer␈αis␈αin␈αthe␈αenclosed␈αenvelope.␈α No-one
␈↓ ↓H␈↓has␈α∞been␈α∞able␈α∞to␈α∞≡nd␈α∞it,␈α∞but␈α∞I␈α∞am␈α∞sure␈α∞that␈α∞if␈α∞you␈α∞put␈α∞it␈α∞in␈α∞your␈α∞column␈α∞a␈α∞number␈α∂of␈α∞people,
␈↓ ↓H␈↓besides␈αthose␈αI␈αhave␈αtold,␈αwill␈α≡nd␈αit.␈α It␈αis␈αinteresting␈αto␈αknow␈αif␈αit␈αis␈αcommon␈αknowledge␈αamong
␈↓ ↓H␈↓the inhabitants of the places.


␈↓ ↓H␈↓Sincerely,



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

␈↓ ↓H␈↓Enclosure:  Envelope