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0 := {x: x ={y: ~(y = y)}}
1 := {x: y(yεx.&.x\{y}ε0)}
2 := {x: y(yεx.&.x\{y}ε1)}
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0:= â§, 1:= {â§} = {0} =0âª{0},
2:= {â§,{â§}} = {0,1} = 1âª{1}
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= 1+0* (å 为 1:= 0*)
= (1+0)* (æ ¹æ®æ¡ä»¶(2))
= 1* (æ ¹æ®æ¡ä»¶(1))
= 2 (å 为 2:= 1*)
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αε1 (âx)(α={x})
βε2 (âx)(ây)(β={x,y}.&.~(x=y))
ξε1+1 (âx)(ây)(β={x}âª{y}.&.~(x=y))
æ以对äºä»»æçéåγï¼æ们æ
γε1+1
(âx)(ây)(γ={x}âª{y}.&.~(x=y))
(âx)(ây)(γ={x,y}.&.~(x=y))
γε2
æ ¹æ®éå论çå¤å»¶å
¬ç(Axiom of Extension)ï¼æ们å¾å°1+1 = 2
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