Is R^n x R^m Isomorphic to R^{n+m}?

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Discussion Overview

The discussion centers around the question of whether the Cartesian product of two Euclidean spaces, R^n x R^m, is isomorphic to R^{n+m}. Participants explore the nature of isomorphisms in this context, including the definitions and implications of injections and bijections.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes a proof involving injections from R^m and R^n to R^{m+n}, suggesting that the sum of these injections forms an isomorphism.
  • Another participant questions the meaning of "isomorphic," asking whether it refers to a bijection between sets or a specific type of isomorphism related to groups or rings.
  • A participant seeks clarification on the notation \theta_1+\theta_2, indicating a need for more detail on the proposed mapping.
  • One participant clarifies that they mean a bijection between the sets, emphasizing the context of the discussion.
  • Another participant explains that \theta_1+\theta_2 refers to the sum of two functions, providing a specific example of how function addition works.
  • A later reply asserts that any two finite-dimensional commutative vector spaces are naturally isomorphic, suggesting a broader principle that may apply to the current discussion.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and implications of isomorphism, with no consensus reached on the correctness of the initial proof or the nature of the mappings discussed.

Contextual Notes

There are unresolved assumptions regarding the definitions of isomorphism and the specific mathematical context (e.g., vector spaces vs. groups) that may affect the discussion.

yifli
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Here is how I prove it:

Let \theta_1(resp.,\theta_2) be the injection from R^m(resp.,R^n) to R^{m+n}

Since injection is an isomorphism, \theta_1+\theta_2 is the isomorphism

Is this correct?
 
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When you say isomorphic, do you mean does there exist a bijection between the sets? Or are you talking about ring or group isomorphism? I ask this because an isomorphism between sets is a group theory topic, but you posted in the calculus section.
 
And what exactly do you mean with \theta_1+\theta_2?
 
I mean bijection between the sets.
 
sum of two functions. (f+g)(x) = f(x)+g(x)
 
yifli said:
Here is how I prove it:

Let \theta_1(resp.,\theta_2) be the injection from R^m(resp.,R^n) to R^{m+n}

Since injection is an isomorphism, \theta_1+\theta_2 is the isomorphism

Is this correct?

To be more clear, injection \thetais a linear mapping from V_i to \prod{V_i} such that \theta(\alpha_j)=(0,...0,\alpha_j , 0,... ,0)
 
Any 2 finite dimensional commutative vector spaces are naturally isomorphic with each other. A natural isomorphism is obtained by considering the map that sends the basis of one to the other
 

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