# Tour:Isomorphic groups

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WHAT YOU NEED TO DO:
• Understand the definition of isomorphic groups
• Convince yourself of why being isomorphic is an equivalence relation.

## Definition

Two groups $G$ and $H$ are termed isomorphic groups, in symbols $G \cong H$ or $H \cong G$, if there exists an isomorphism of groups from $G$ to $H$.

The relation of being isomorphic is an equivalence relation on groups:

• Reflexivity: The identity map is an isomorphism from any group to itself.
• Symmetry: The inverse of an isomorphism is an isomorphism.
• Transitivity: if $G$ is isomorphic to $H$ and $H$ is isomorphic to $K$, then $G$ is isomorphic to $K$, via the isomorphism obtained by composing the isomorphisms from $G$ to $H$ and from $H$ to $K$.

As far as the group structure is concerned, isomorphic groups behave in exactly the same way, so constructions and properties for groups are all studied upto isomorphism-invariance.

This page is part of the Groupprops Guided tour for beginners (Jump to beginning of tour). If you found anything difficult or unclear, make a note of it; it is likely to be resolved by the end of the tour.
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