# Lattices of Subgroups and Graph

In Dummit and Foote´s Abstract Algebra, when talking about the lattice of subgroups of $A_4$, the authors make the statement that, unlike virtaully all groups, $A_4$ has a planar lattice? My question is

What do they mean when they say virtually all groups? Is there a reference for this statement?

On a somewhat different note, are there classes of graphs which can be realized as the subgroup lattice of some group?

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When I put subgroup lattice planar in Google, this paper is among the first results. – Martin Sleziak Jun 18 '12 at 12:56