Isomorph
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<img class="right" alt="isomorph cats" src="categories/img/isomorph-cats.jpg" />
<em class="yellow">isomorphism</em>:
\\(f:A→B\\) which can be "undone" _i.e._   
\\(∃g:B→A\\), \\(g∘f=id\_A\\) & \\(f∘g=id\_B\\)  
in this case, \\(A\\) &amp; \\(B\\) are <em class="yellow">isomorphic</em>.

<span class="yellow">A≌B</span> means A and B are essentially the same.  
In Category Theory, <span class="yellow">=</span> is in fact mostly <span class="yellow">≌</span>.  
For example in commutative diagrams.