How can I prove this proposition from Peano Axioms: (Cancellation law). Let a, b, c be natural numbers such that a + b = a + c. Then we have b = c.

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Peano Axioms.



Axiom 2.1



$0$ is a natural number.



Axiom 2.2



If $n$ is a natural number then $n++$ is also a natural number. (Here $n++$
denotes the successor of $n$ and previously in the book the notational
implication has been bijected to the familiar $1,2…$).



Axiom 2.3



$0$ is not the successor of natural number; i.e. we have $n++≠0$ for every
natural number $n$.



Axiom 2.4



Different natural numbers must have different successors; i.e., if $n,m$
are natural numbers and $n≠m$, then $n++≠m++$.



Axiom 2.5



Let $P(n)$ be any property pertaining to a natural number $n$. Suppose
that $P(0)$ is true, and suppose that whenever $P(n)$ is true, $P(n++)$ is
also true. Then $P(n)$ is true for every natural number $n$.



Definition of Addition: Let m be a natural number. We define, $0+m=m$
and suppose we have inductively defined the addtion $n+m$ then we
define, $(n++)+m=(n+m)++$. Where $n++$ is the successor of $n$.




Terence Tao has a proof in his Analysis I book, but I couldn't understand . I want a proof line by line like this:



Thm: 3 is a natural number
beginalign*
& 0 text is natural && textAxiom 2.1 \
& 0++ = 1 text is natural && textAxiom 2.2\
& 1++ = 2 text is natural && textAxiom 2.2\
& 2++ = 3 text is natural && textAxiom 2.2
endalign*







share|cite|improve this question

















  • 2




    What have you proven so far? Have you shown commutativity?
    – InterstellarProbe
    Jul 31 at 13:52














up vote
1
down vote

favorite













Peano Axioms.



Axiom 2.1



$0$ is a natural number.



Axiom 2.2



If $n$ is a natural number then $n++$ is also a natural number. (Here $n++$
denotes the successor of $n$ and previously in the book the notational
implication has been bijected to the familiar $1,2…$).



Axiom 2.3



$0$ is not the successor of natural number; i.e. we have $n++≠0$ for every
natural number $n$.



Axiom 2.4



Different natural numbers must have different successors; i.e., if $n,m$
are natural numbers and $n≠m$, then $n++≠m++$.



Axiom 2.5



Let $P(n)$ be any property pertaining to a natural number $n$. Suppose
that $P(0)$ is true, and suppose that whenever $P(n)$ is true, $P(n++)$ is
also true. Then $P(n)$ is true for every natural number $n$.



Definition of Addition: Let m be a natural number. We define, $0+m=m$
and suppose we have inductively defined the addtion $n+m$ then we
define, $(n++)+m=(n+m)++$. Where $n++$ is the successor of $n$.




Terence Tao has a proof in his Analysis I book, but I couldn't understand . I want a proof line by line like this:



Thm: 3 is a natural number
beginalign*
& 0 text is natural && textAxiom 2.1 \
& 0++ = 1 text is natural && textAxiom 2.2\
& 1++ = 2 text is natural && textAxiom 2.2\
& 2++ = 3 text is natural && textAxiom 2.2
endalign*







share|cite|improve this question

















  • 2




    What have you proven so far? Have you shown commutativity?
    – InterstellarProbe
    Jul 31 at 13:52












up vote
1
down vote

favorite









up vote
1
down vote

favorite












Peano Axioms.



Axiom 2.1



$0$ is a natural number.



Axiom 2.2



If $n$ is a natural number then $n++$ is also a natural number. (Here $n++$
denotes the successor of $n$ and previously in the book the notational
implication has been bijected to the familiar $1,2…$).



Axiom 2.3



$0$ is not the successor of natural number; i.e. we have $n++≠0$ for every
natural number $n$.



Axiom 2.4



Different natural numbers must have different successors; i.e., if $n,m$
are natural numbers and $n≠m$, then $n++≠m++$.



Axiom 2.5



Let $P(n)$ be any property pertaining to a natural number $n$. Suppose
that $P(0)$ is true, and suppose that whenever $P(n)$ is true, $P(n++)$ is
also true. Then $P(n)$ is true for every natural number $n$.



Definition of Addition: Let m be a natural number. We define, $0+m=m$
and suppose we have inductively defined the addtion $n+m$ then we
define, $(n++)+m=(n+m)++$. Where $n++$ is the successor of $n$.




Terence Tao has a proof in his Analysis I book, but I couldn't understand . I want a proof line by line like this:



Thm: 3 is a natural number
beginalign*
& 0 text is natural && textAxiom 2.1 \
& 0++ = 1 text is natural && textAxiom 2.2\
& 1++ = 2 text is natural && textAxiom 2.2\
& 2++ = 3 text is natural && textAxiom 2.2
endalign*







share|cite|improve this question














Peano Axioms.



Axiom 2.1



$0$ is a natural number.



Axiom 2.2



If $n$ is a natural number then $n++$ is also a natural number. (Here $n++$
denotes the successor of $n$ and previously in the book the notational
implication has been bijected to the familiar $1,2…$).



Axiom 2.3



$0$ is not the successor of natural number; i.e. we have $n++≠0$ for every
natural number $n$.



Axiom 2.4



Different natural numbers must have different successors; i.e., if $n,m$
are natural numbers and $n≠m$, then $n++≠m++$.



Axiom 2.5



Let $P(n)$ be any property pertaining to a natural number $n$. Suppose
that $P(0)$ is true, and suppose that whenever $P(n)$ is true, $P(n++)$ is
also true. Then $P(n)$ is true for every natural number $n$.



Definition of Addition: Let m be a natural number. We define, $0+m=m$
and suppose we have inductively defined the addtion $n+m$ then we
define, $(n++)+m=(n+m)++$. Where $n++$ is the successor of $n$.




Terence Tao has a proof in his Analysis I book, but I couldn't understand . I want a proof line by line like this:



Thm: 3 is a natural number
beginalign*
& 0 text is natural && textAxiom 2.1 \
& 0++ = 1 text is natural && textAxiom 2.2\
& 1++ = 2 text is natural && textAxiom 2.2\
& 2++ = 3 text is natural && textAxiom 2.2
endalign*









share|cite|improve this question












share|cite|improve this question




share|cite|improve this question








edited Aug 1 at 11:55









user529760

509216




509216









asked Jul 31 at 13:47









Henrique

82




82







  • 2




    What have you proven so far? Have you shown commutativity?
    – InterstellarProbe
    Jul 31 at 13:52












  • 2




    What have you proven so far? Have you shown commutativity?
    – InterstellarProbe
    Jul 31 at 13:52







2




2




What have you proven so far? Have you shown commutativity?
– InterstellarProbe
Jul 31 at 13:52




What have you proven so far? Have you shown commutativity?
– InterstellarProbe
Jul 31 at 13:52










2 Answers
2






active

oldest

votes

















up vote
3
down vote



accepted










The proof is by induction on $a$.



Basis [case with $a=0$]. We want to prove that :




if $0+b=0+c$, then $b=c$.




But we have that : $0+b=b$, by definition of addition.



And also : $0+c=c$.



Thus, by transitivity of equality : $b=c$.




Induction step. Assume that the property holds for $a$ and prove it for $a'$ [I prefer to use $a'$ instead of $a++$ for the successor of $a$].



This means :




assume that "if $a+b=a+c$, then $b=c$" holds, and prove that "if $a'+b=a'+c$, then $b=c$" holds.




We have $a'+b=(a+b)'$ by definition of addition.



And $a'+c=(a+c)’$, by definition of addition.



We assume that : $a'+b=a'+c$, and thus, again by transitivity of equality, we have that : $(a+b)'=(a+c)'$.



By axiom 2.4 (different numbers have different successors), by contraposition, we conclude that $(a+b)=(a+c)$.



Thus, applying induction hypothesis, we have that :




$b=c$.






The general strategy used above in order to prove "if $P$, then $Q$", is to assume $P$ and derive $Q$.



This type of proof is called Conditional Proof; we can see it above :



1) if $a+b=a+c$, then $b=c$ --- induction hypothesis



2) $a'+b=a'+c$ --- assumption for CP



3) $(a+b)'=(a+c)'$ --- from 2) and definition of addition and tarnsitivity of equality



4) $a+b=a+c$ --- from 3) and axiom 2.4 by Contraposition [the axiom says : "if $(a+b ne a+c)$, then $(a+b)' ne (a+c)'$"; thus, contraposing it we get : "if $(a+b)' = (a+c)'$, then $(a+b) = (a+c)$"] and Modus ponens



5) $b=c$ --- from 4) and 1) by Modus ponens (also called : detachment)




6) if $a'+b=a'+c$, then $b=c$ --- from 2) and 5) by Conditional Proof.







share|cite|improve this answer



















  • 1




    (In your last yellow box before the general strategy, it should be $b=c$)
    – Jason DeVito
    Jul 31 at 14:31










  • Thanks! Amazing.
    – Henrique
    Jul 31 at 15:25

















up vote
0
down vote













Here is a formal proof done in Fitch:



(Note: I use $s(x)$ instead of $x$++)



enter image description here






share|cite|improve this answer





















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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes








    up vote
    3
    down vote



    accepted










    The proof is by induction on $a$.



    Basis [case with $a=0$]. We want to prove that :




    if $0+b=0+c$, then $b=c$.




    But we have that : $0+b=b$, by definition of addition.



    And also : $0+c=c$.



    Thus, by transitivity of equality : $b=c$.




    Induction step. Assume that the property holds for $a$ and prove it for $a'$ [I prefer to use $a'$ instead of $a++$ for the successor of $a$].



    This means :




    assume that "if $a+b=a+c$, then $b=c$" holds, and prove that "if $a'+b=a'+c$, then $b=c$" holds.




    We have $a'+b=(a+b)'$ by definition of addition.



    And $a'+c=(a+c)’$, by definition of addition.



    We assume that : $a'+b=a'+c$, and thus, again by transitivity of equality, we have that : $(a+b)'=(a+c)'$.



    By axiom 2.4 (different numbers have different successors), by contraposition, we conclude that $(a+b)=(a+c)$.



    Thus, applying induction hypothesis, we have that :




    $b=c$.






    The general strategy used above in order to prove "if $P$, then $Q$", is to assume $P$ and derive $Q$.



    This type of proof is called Conditional Proof; we can see it above :



    1) if $a+b=a+c$, then $b=c$ --- induction hypothesis



    2) $a'+b=a'+c$ --- assumption for CP



    3) $(a+b)'=(a+c)'$ --- from 2) and definition of addition and tarnsitivity of equality



    4) $a+b=a+c$ --- from 3) and axiom 2.4 by Contraposition [the axiom says : "if $(a+b ne a+c)$, then $(a+b)' ne (a+c)'$"; thus, contraposing it we get : "if $(a+b)' = (a+c)'$, then $(a+b) = (a+c)$"] and Modus ponens



    5) $b=c$ --- from 4) and 1) by Modus ponens (also called : detachment)




    6) if $a'+b=a'+c$, then $b=c$ --- from 2) and 5) by Conditional Proof.







    share|cite|improve this answer



















    • 1




      (In your last yellow box before the general strategy, it should be $b=c$)
      – Jason DeVito
      Jul 31 at 14:31










    • Thanks! Amazing.
      – Henrique
      Jul 31 at 15:25














    up vote
    3
    down vote



    accepted










    The proof is by induction on $a$.



    Basis [case with $a=0$]. We want to prove that :




    if $0+b=0+c$, then $b=c$.




    But we have that : $0+b=b$, by definition of addition.



    And also : $0+c=c$.



    Thus, by transitivity of equality : $b=c$.




    Induction step. Assume that the property holds for $a$ and prove it for $a'$ [I prefer to use $a'$ instead of $a++$ for the successor of $a$].



    This means :




    assume that "if $a+b=a+c$, then $b=c$" holds, and prove that "if $a'+b=a'+c$, then $b=c$" holds.




    We have $a'+b=(a+b)'$ by definition of addition.



    And $a'+c=(a+c)’$, by definition of addition.



    We assume that : $a'+b=a'+c$, and thus, again by transitivity of equality, we have that : $(a+b)'=(a+c)'$.



    By axiom 2.4 (different numbers have different successors), by contraposition, we conclude that $(a+b)=(a+c)$.



    Thus, applying induction hypothesis, we have that :




    $b=c$.






    The general strategy used above in order to prove "if $P$, then $Q$", is to assume $P$ and derive $Q$.



    This type of proof is called Conditional Proof; we can see it above :



    1) if $a+b=a+c$, then $b=c$ --- induction hypothesis



    2) $a'+b=a'+c$ --- assumption for CP



    3) $(a+b)'=(a+c)'$ --- from 2) and definition of addition and tarnsitivity of equality



    4) $a+b=a+c$ --- from 3) and axiom 2.4 by Contraposition [the axiom says : "if $(a+b ne a+c)$, then $(a+b)' ne (a+c)'$"; thus, contraposing it we get : "if $(a+b)' = (a+c)'$, then $(a+b) = (a+c)$"] and Modus ponens



    5) $b=c$ --- from 4) and 1) by Modus ponens (also called : detachment)




    6) if $a'+b=a'+c$, then $b=c$ --- from 2) and 5) by Conditional Proof.







    share|cite|improve this answer



















    • 1




      (In your last yellow box before the general strategy, it should be $b=c$)
      – Jason DeVito
      Jul 31 at 14:31










    • Thanks! Amazing.
      – Henrique
      Jul 31 at 15:25












    up vote
    3
    down vote



    accepted







    up vote
    3
    down vote



    accepted






    The proof is by induction on $a$.



    Basis [case with $a=0$]. We want to prove that :




    if $0+b=0+c$, then $b=c$.




    But we have that : $0+b=b$, by definition of addition.



    And also : $0+c=c$.



    Thus, by transitivity of equality : $b=c$.




    Induction step. Assume that the property holds for $a$ and prove it for $a'$ [I prefer to use $a'$ instead of $a++$ for the successor of $a$].



    This means :




    assume that "if $a+b=a+c$, then $b=c$" holds, and prove that "if $a'+b=a'+c$, then $b=c$" holds.




    We have $a'+b=(a+b)'$ by definition of addition.



    And $a'+c=(a+c)’$, by definition of addition.



    We assume that : $a'+b=a'+c$, and thus, again by transitivity of equality, we have that : $(a+b)'=(a+c)'$.



    By axiom 2.4 (different numbers have different successors), by contraposition, we conclude that $(a+b)=(a+c)$.



    Thus, applying induction hypothesis, we have that :




    $b=c$.






    The general strategy used above in order to prove "if $P$, then $Q$", is to assume $P$ and derive $Q$.



    This type of proof is called Conditional Proof; we can see it above :



    1) if $a+b=a+c$, then $b=c$ --- induction hypothesis



    2) $a'+b=a'+c$ --- assumption for CP



    3) $(a+b)'=(a+c)'$ --- from 2) and definition of addition and tarnsitivity of equality



    4) $a+b=a+c$ --- from 3) and axiom 2.4 by Contraposition [the axiom says : "if $(a+b ne a+c)$, then $(a+b)' ne (a+c)'$"; thus, contraposing it we get : "if $(a+b)' = (a+c)'$, then $(a+b) = (a+c)$"] and Modus ponens



    5) $b=c$ --- from 4) and 1) by Modus ponens (also called : detachment)




    6) if $a'+b=a'+c$, then $b=c$ --- from 2) and 5) by Conditional Proof.







    share|cite|improve this answer















    The proof is by induction on $a$.



    Basis [case with $a=0$]. We want to prove that :




    if $0+b=0+c$, then $b=c$.




    But we have that : $0+b=b$, by definition of addition.



    And also : $0+c=c$.



    Thus, by transitivity of equality : $b=c$.




    Induction step. Assume that the property holds for $a$ and prove it for $a'$ [I prefer to use $a'$ instead of $a++$ for the successor of $a$].



    This means :




    assume that "if $a+b=a+c$, then $b=c$" holds, and prove that "if $a'+b=a'+c$, then $b=c$" holds.




    We have $a'+b=(a+b)'$ by definition of addition.



    And $a'+c=(a+c)’$, by definition of addition.



    We assume that : $a'+b=a'+c$, and thus, again by transitivity of equality, we have that : $(a+b)'=(a+c)'$.



    By axiom 2.4 (different numbers have different successors), by contraposition, we conclude that $(a+b)=(a+c)$.



    Thus, applying induction hypothesis, we have that :




    $b=c$.






    The general strategy used above in order to prove "if $P$, then $Q$", is to assume $P$ and derive $Q$.



    This type of proof is called Conditional Proof; we can see it above :



    1) if $a+b=a+c$, then $b=c$ --- induction hypothesis



    2) $a'+b=a'+c$ --- assumption for CP



    3) $(a+b)'=(a+c)'$ --- from 2) and definition of addition and tarnsitivity of equality



    4) $a+b=a+c$ --- from 3) and axiom 2.4 by Contraposition [the axiom says : "if $(a+b ne a+c)$, then $(a+b)' ne (a+c)'$"; thus, contraposing it we get : "if $(a+b)' = (a+c)'$, then $(a+b) = (a+c)$"] and Modus ponens



    5) $b=c$ --- from 4) and 1) by Modus ponens (also called : detachment)




    6) if $a'+b=a'+c$, then $b=c$ --- from 2) and 5) by Conditional Proof.








    share|cite|improve this answer















    share|cite|improve this answer



    share|cite|improve this answer








    edited Aug 1 at 10:42


























    answered Jul 31 at 13:57









    Mauro ALLEGRANZA

    60.6k346105




    60.6k346105







    • 1




      (In your last yellow box before the general strategy, it should be $b=c$)
      – Jason DeVito
      Jul 31 at 14:31










    • Thanks! Amazing.
      – Henrique
      Jul 31 at 15:25












    • 1




      (In your last yellow box before the general strategy, it should be $b=c$)
      – Jason DeVito
      Jul 31 at 14:31










    • Thanks! Amazing.
      – Henrique
      Jul 31 at 15:25







    1




    1




    (In your last yellow box before the general strategy, it should be $b=c$)
    – Jason DeVito
    Jul 31 at 14:31




    (In your last yellow box before the general strategy, it should be $b=c$)
    – Jason DeVito
    Jul 31 at 14:31












    Thanks! Amazing.
    – Henrique
    Jul 31 at 15:25




    Thanks! Amazing.
    – Henrique
    Jul 31 at 15:25










    up vote
    0
    down vote













    Here is a formal proof done in Fitch:



    (Note: I use $s(x)$ instead of $x$++)



    enter image description here






    share|cite|improve this answer

























      up vote
      0
      down vote













      Here is a formal proof done in Fitch:



      (Note: I use $s(x)$ instead of $x$++)



      enter image description here






      share|cite|improve this answer























        up vote
        0
        down vote










        up vote
        0
        down vote









        Here is a formal proof done in Fitch:



        (Note: I use $s(x)$ instead of $x$++)



        enter image description here






        share|cite|improve this answer













        Here is a formal proof done in Fitch:



        (Note: I use $s(x)$ instead of $x$++)



        enter image description here







        share|cite|improve this answer













        share|cite|improve this answer



        share|cite|improve this answer











        answered Jul 31 at 18:26









        Bram28

        54.6k33880




        54.6k33880






















             

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