I want this but when I am writing

$$x\in\mathcal{W}_{i+1}\Leftrightarrow \exists y\in\mathcal{W}_i : Ex = Ay = (A-\lambda E)y +\lambda Ey$$
$$\Leftrightarrow \exists y\in\mathcal{W}_i = \ker \hat{E}^i : \hat{E}x = (I + \lambda \hat{E})y =: \hat{y}$$
$$\Leftrightarrow \exists \hat{y}\in\ker\hat{E}^i : \hat{E}x = \hat{y}$$
$$\Leftrightarrow x\in \ker \hat{E}^ {i+1}$$ .

I am getting this

enter image description here

  • You might like to have a quick read of this post tex.stackexchange.com/questions/503/why-is-preferable-to to see why we usually recommend avoiding $$ ... $$ and using \[ ... \] instead. Anyway, you need to use some kind of align environment – Au101 Nov 7 '16 at 22:28
  • \begin{align*} x\in\mathcal{W}_{i+1}&\Leftrightarrow \exists ... \\ &\Leftrightarrow \exists y \in ... \\ &\Leftrightarrow ... ... \end{align*} – Au101 Nov 7 '16 at 22:29

Use the align environment.


x\in\mathcal{W}_{i+1}&\Longleftrightarrow \exists y\in\mathcal{W}_i : Ex = Ay = (A-\lambda E)y +\lambda Ey\\
&\Longleftrightarrow \exists y\in\mathcal{W}_i = \ker \hat{E}^i : \hat{E}x = (I + \lambda \hat{E})y =: \hat{y}\\
&\Longleftrightarrow \exists \hat{y}\in\ker\hat{E}^i : \hat{E}x = \hat{y}\\
&\Longleftrightarrow x\in \ker \hat{E}^ {i+1}.\quad  \square

This yields:

enter image description here

I also added the code for a square \square

  • I was about thirty seconds behind you. +1 Only recommendation is you replace all of those escaped spaces with something like \quad or \qquad – Au101 Nov 7 '16 at 22:35
  • @Au101 Good idea, I wasn't aware of \quad. I just edited my answer to include it. Thanks – Dan Nov 7 '16 at 22:39
  • Also I was going to suggest using \Longleftrightarrow (possibly with a semantically meaningful abbreviation defined as it's rather unwieldy) as it's closer to the symbol in the original. Seems a bit pointless me putting that as a separate answer, but you could include it as a recommendation if you wanted to – Au101 Nov 7 '16 at 22:39
  • Here you go :) tex.stackexchange.com/questions/119068/meaning-of-quad – Au101 Nov 7 '16 at 22:39
  • @Au101 Thanks again. I added the \Longleftrightarrow. – Dan Nov 7 '16 at 22:44

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