Archimedean equivalence. Proof of $ [g+h] geq min{ [g], [h] }$












0












$begingroup$



Prove that: $ [g+h] geq min{[g],[h]}$




Definitons:
Take any ordered abelian field $(G, leq)$. Two elements $g,h in G$ are archimedean equivalent if $exists n,n' in Bbb{N}$ : $n|g| geq |h|$ and $n'|h| geq |g|$.
$[g]$ denotes the equivalence class of $g$.



Attempt of proof:
Suppose that $ min{ [g], [h] }= [h]$



$[h] = {g: exists n_1, n_1' $such that$ n_1|h| geq |g| $and$ n_1'|g| geq |h|} $



$[h+g] ={ k: exists n_2, n_2' $such that$ n_2|g+h| geq |k| $and$ n_2'|k| geq |g+h| }$



I have to show that $k>g$ so I have to show that $ng<k$ for all $n in Bbb{N}$. From my assumption $[h] < [g]$ so it implies $|h| > |g|$ and $[g] neq[h]$. I am not sure what to do know. I have tried to multiply these inequalities by an inverse element for example of $n_1, n_1'$. I can also use the fact: $[g] geq [h]$ for all $h in G$ iff $g=0$.










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$endgroup$












  • $begingroup$
    Use $min$ for $min$.
    $endgroup$
    – Shaun
    Jan 22 at 15:46
















0












$begingroup$



Prove that: $ [g+h] geq min{[g],[h]}$




Definitons:
Take any ordered abelian field $(G, leq)$. Two elements $g,h in G$ are archimedean equivalent if $exists n,n' in Bbb{N}$ : $n|g| geq |h|$ and $n'|h| geq |g|$.
$[g]$ denotes the equivalence class of $g$.



Attempt of proof:
Suppose that $ min{ [g], [h] }= [h]$



$[h] = {g: exists n_1, n_1' $such that$ n_1|h| geq |g| $and$ n_1'|g| geq |h|} $



$[h+g] ={ k: exists n_2, n_2' $such that$ n_2|g+h| geq |k| $and$ n_2'|k| geq |g+h| }$



I have to show that $k>g$ so I have to show that $ng<k$ for all $n in Bbb{N}$. From my assumption $[h] < [g]$ so it implies $|h| > |g|$ and $[g] neq[h]$. I am not sure what to do know. I have tried to multiply these inequalities by an inverse element for example of $n_1, n_1'$. I can also use the fact: $[g] geq [h]$ for all $h in G$ iff $g=0$.










share|cite|improve this question











$endgroup$












  • $begingroup$
    Use $min$ for $min$.
    $endgroup$
    – Shaun
    Jan 22 at 15:46














0












0








0





$begingroup$



Prove that: $ [g+h] geq min{[g],[h]}$




Definitons:
Take any ordered abelian field $(G, leq)$. Two elements $g,h in G$ are archimedean equivalent if $exists n,n' in Bbb{N}$ : $n|g| geq |h|$ and $n'|h| geq |g|$.
$[g]$ denotes the equivalence class of $g$.



Attempt of proof:
Suppose that $ min{ [g], [h] }= [h]$



$[h] = {g: exists n_1, n_1' $such that$ n_1|h| geq |g| $and$ n_1'|g| geq |h|} $



$[h+g] ={ k: exists n_2, n_2' $such that$ n_2|g+h| geq |k| $and$ n_2'|k| geq |g+h| }$



I have to show that $k>g$ so I have to show that $ng<k$ for all $n in Bbb{N}$. From my assumption $[h] < [g]$ so it implies $|h| > |g|$ and $[g] neq[h]$. I am not sure what to do know. I have tried to multiply these inequalities by an inverse element for example of $n_1, n_1'$. I can also use the fact: $[g] geq [h]$ for all $h in G$ iff $g=0$.










share|cite|improve this question











$endgroup$





Prove that: $ [g+h] geq min{[g],[h]}$




Definitons:
Take any ordered abelian field $(G, leq)$. Two elements $g,h in G$ are archimedean equivalent if $exists n,n' in Bbb{N}$ : $n|g| geq |h|$ and $n'|h| geq |g|$.
$[g]$ denotes the equivalence class of $g$.



Attempt of proof:
Suppose that $ min{ [g], [h] }= [h]$



$[h] = {g: exists n_1, n_1' $such that$ n_1|h| geq |g| $and$ n_1'|g| geq |h|} $



$[h+g] ={ k: exists n_2, n_2' $such that$ n_2|g+h| geq |k| $and$ n_2'|k| geq |g+h| }$



I have to show that $k>g$ so I have to show that $ng<k$ for all $n in Bbb{N}$. From my assumption $[h] < [g]$ so it implies $|h| > |g|$ and $[g] neq[h]$. I am not sure what to do know. I have tried to multiply these inequalities by an inverse element for example of $n_1, n_1'$. I can also use the fact: $[g] geq [h]$ for all $h in G$ iff $g=0$.







real-analysis order-theory






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edited Jan 22 at 17:32







Hikicianka

















asked Jan 22 at 15:39









HikiciankaHikicianka

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1498












  • $begingroup$
    Use $min$ for $min$.
    $endgroup$
    – Shaun
    Jan 22 at 15:46


















  • $begingroup$
    Use $min$ for $min$.
    $endgroup$
    – Shaun
    Jan 22 at 15:46
















$begingroup$
Use $min$ for $min$.
$endgroup$
– Shaun
Jan 22 at 15:46




$begingroup$
Use $min$ for $min$.
$endgroup$
– Shaun
Jan 22 at 15:46










1 Answer
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$begingroup$

Assume that $ [g+h] < min([g],[h]) $. Let $ [g] = min([g], [h]) Longrightarrow [g] > [h] Longleftrightarrow forall_{n in mathbb{N}} ; |g| > n|h|$.

From assumption we have $ ; [g + h] < [g] Longrightarrow |g| < |g + h| ; text{and} ; [g + h] neq [g] $.

We know that
$$
|g| < |g + h| Longleftrightarrow forall_{n in mathbb{N}} ; n|g| < |g + h| leq |g| + |h| Longrightarrow (n - 1)|g| < |g + h| - |g| leq |h| \
Longrightarrow (n - 1)|g| < |h|
$$

So we have $$forall_{n in mathbb{N}} ; (n - 1)|g| < |h| quad wedge quad |g| > n|h| $$
Hence it doesn't true then $ [g+h] geq min([g],[h]) $. $square$






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    $begingroup$

    Assume that $ [g+h] < min([g],[h]) $. Let $ [g] = min([g], [h]) Longrightarrow [g] > [h] Longleftrightarrow forall_{n in mathbb{N}} ; |g| > n|h|$.

    From assumption we have $ ; [g + h] < [g] Longrightarrow |g| < |g + h| ; text{and} ; [g + h] neq [g] $.

    We know that
    $$
    |g| < |g + h| Longleftrightarrow forall_{n in mathbb{N}} ; n|g| < |g + h| leq |g| + |h| Longrightarrow (n - 1)|g| < |g + h| - |g| leq |h| \
    Longrightarrow (n - 1)|g| < |h|
    $$

    So we have $$forall_{n in mathbb{N}} ; (n - 1)|g| < |h| quad wedge quad |g| > n|h| $$
    Hence it doesn't true then $ [g+h] geq min([g],[h]) $. $square$






    share|cite|improve this answer









    $endgroup$


















      1












      $begingroup$

      Assume that $ [g+h] < min([g],[h]) $. Let $ [g] = min([g], [h]) Longrightarrow [g] > [h] Longleftrightarrow forall_{n in mathbb{N}} ; |g| > n|h|$.

      From assumption we have $ ; [g + h] < [g] Longrightarrow |g| < |g + h| ; text{and} ; [g + h] neq [g] $.

      We know that
      $$
      |g| < |g + h| Longleftrightarrow forall_{n in mathbb{N}} ; n|g| < |g + h| leq |g| + |h| Longrightarrow (n - 1)|g| < |g + h| - |g| leq |h| \
      Longrightarrow (n - 1)|g| < |h|
      $$

      So we have $$forall_{n in mathbb{N}} ; (n - 1)|g| < |h| quad wedge quad |g| > n|h| $$
      Hence it doesn't true then $ [g+h] geq min([g],[h]) $. $square$






      share|cite|improve this answer









      $endgroup$
















        1












        1








        1





        $begingroup$

        Assume that $ [g+h] < min([g],[h]) $. Let $ [g] = min([g], [h]) Longrightarrow [g] > [h] Longleftrightarrow forall_{n in mathbb{N}} ; |g| > n|h|$.

        From assumption we have $ ; [g + h] < [g] Longrightarrow |g| < |g + h| ; text{and} ; [g + h] neq [g] $.

        We know that
        $$
        |g| < |g + h| Longleftrightarrow forall_{n in mathbb{N}} ; n|g| < |g + h| leq |g| + |h| Longrightarrow (n - 1)|g| < |g + h| - |g| leq |h| \
        Longrightarrow (n - 1)|g| < |h|
        $$

        So we have $$forall_{n in mathbb{N}} ; (n - 1)|g| < |h| quad wedge quad |g| > n|h| $$
        Hence it doesn't true then $ [g+h] geq min([g],[h]) $. $square$






        share|cite|improve this answer









        $endgroup$



        Assume that $ [g+h] < min([g],[h]) $. Let $ [g] = min([g], [h]) Longrightarrow [g] > [h] Longleftrightarrow forall_{n in mathbb{N}} ; |g| > n|h|$.

        From assumption we have $ ; [g + h] < [g] Longrightarrow |g| < |g + h| ; text{and} ; [g + h] neq [g] $.

        We know that
        $$
        |g| < |g + h| Longleftrightarrow forall_{n in mathbb{N}} ; n|g| < |g + h| leq |g| + |h| Longrightarrow (n - 1)|g| < |g + h| - |g| leq |h| \
        Longrightarrow (n - 1)|g| < |h|
        $$

        So we have $$forall_{n in mathbb{N}} ; (n - 1)|g| < |h| quad wedge quad |g| > n|h| $$
        Hence it doesn't true then $ [g+h] geq min([g],[h]) $. $square$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Feb 6 at 19:39









        nowek7nowek7

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