Marshallprovidednogeometricproof,,.[12],supposethehorizontalaxisoffigure4measuresnotonlylaborbutnonlandinputsingeneral（andassumeawaytheassociatedsubstitutionproblem）.（notany）rentalpercentage,andgiventhatthelandlordhasbeenprovidingasufficientlylargeamountofnonland"capital"input,thenhemayadjustthenonlandinputsprovidedbyeithercontractingpartysothat（a）therentalineundersharerentisthesameasunderfixedrentand（b）thetenant',-videallthenonlandinputs,orthatthelandlordhasbeenprovid-ingapartofthenonlandinputsbuttheamountistoosmall;then,exceptbyaccident,therentalpercentagemustbevaried（inadditiontoadjustingnonlandinputsoverland）:giventheratioofnonlandinputstolandthatisconsistentwithwealthmaximization,andgiventhattherelativesharesofnonlandinputscontributedbythecontractingpartiesarestipulated,thereexistsoneandonlyonerentalpercentagewhichisconsistentwithequilibrium.[13],likeSmith,Jones,andMillbeforehim,attemptedto"rank"variouslandtenurearrangementsaccordingtosomenotionofeconomicefficiency.[14],thefreelyalienablerightsimplicitintheiranalysessuggestthattheconstraintofprivatepropertyrightswasassumed.[15]ButwhereasSmithandJonesviewedasharelease,thoughwasteful,"custom."Smith'spredictionthatfixedrentswouldreplacesharerentshadfailedtoetrue;and,asnotedearlier,"rank-ings"andalsoreliedonthenotionof"custom"areRainerSchic-kele[16].[17]SchickeleandHeadyfurtheredthetaxapproachintheiranalysesofasharelease,butinawaysomewhatdifferentfromMarshall.Usingadiagramidenticaltofigure4,theyconcludedthatequilibriumisatpoints,wherethemarginaltenantcostequalsthemarginaltenantreceipt;thatis,

=

（1-r）.,iftenantinputisincreasedfromt1tot2,thenareaABCrepresentsa"present"fromthetenanttothelandowner[18]—sincetheaddedtenantreceipt（areat1ACt2）islessthantheaddedtenantcost（areat1ABt2）,however,proceedwiththeparadox:iftenantinputisatt1,thenareaMEA（tenant'sresidualearning）representsa"present"fromthelandownertothetenant.Itfollowsfromthislineofreasoningthatiftenantinputissomewherebetweent1andt2,bothpartieswillbeoffering"presents"toeachother!