▁rig or ▁of ▁rival ▁research ers , ▁ ▁including ▁Ed win ▁Robert ▁Anderson ▁Sel ig man , ▁a ▁noted ▁ske ptic ▁of ▁mathematical ▁econom ics . ▁ ▁The ▁articles ▁focused ▁on ▁a ▁back ▁and ▁forth ▁over ▁tax ▁inc idence ▁and ▁responses ▁by ▁produ cers . ▁ ▁Ed gew orth ▁noticed ▁that ▁a ▁mon opol y ▁producing ▁a ▁good ▁that ▁had ▁joint ness ▁of ▁supply ▁but ▁not ▁joint ness ▁of ▁demand ▁( such ▁as ▁first ▁class ▁and ▁economy ▁on ▁an ▁air plane , ▁if ▁the ▁plane ▁f lies , ▁both ▁sets ▁of ▁seats ▁fly ▁with ▁it ) ▁might ▁actually ▁lower ▁the ▁price ▁seen ▁by ▁the ▁consumer ▁for ▁one ▁of ▁the ▁two ▁comm od ities ▁if ▁a ▁tax ▁were ▁applied . ▁ ▁Common ▁sense ▁and ▁more ▁traditional , ▁numerical ▁analysis ▁seemed ▁to ▁indicate ▁that ▁this ▁was ▁pre post er ous . ▁ ▁Sel ig man ▁ins isted ▁that ▁the ▁results ▁Ed gew orth ▁achieved ▁were ▁a ▁qu irk ▁of ▁his ▁mathematical ▁form ulation . ▁ ▁He ▁suggested ▁that ▁the ▁assumption ▁of ▁a ▁continuous ▁demand ▁function ▁and ▁an ▁inf init es imal ▁change ▁in ▁the ▁tax ▁resulted ▁in ▁the ▁par ado x ical ▁predictions . ▁ ▁Harold ▁Hot elling ▁later ▁showed ▁that ▁Ed gew orth ▁was ▁correct ▁and ▁that ▁the ▁same ▁result ▁( a ▁" dim in ution ▁of ▁price ▁as ▁a ▁result ▁of ▁the ▁tax ") ▁could ▁occur ▁with ▁a ▁dis continu ous ▁demand ▁function ▁and ▁large ▁changes ▁in ▁the ▁tax ▁rate . ▁ ▁Modern ▁mathematical ▁econom ics ▁From ▁the ▁later - 1 9 3