= Solution
A typical <globular cluster> has undergone appreciable <two-body relaxation>, since its <stellar relaxation time> is $t_{\rm rel}\sim0.1(N/\ln N)t_{\rm cross}$: for $N\sim10^5$ and <stellar crossing time> $t_{\rm cross}\sim10^6\,\mathrm{yr}$ this is about $10^9\,\mathrm{yr}$, shorter than its age, allowing a relatively relaxed, tidally limited structure. A <galaxy> with $N\sim10^{11}$ and $t_{\rm cross}\sim10^8\,\mathrm{yr}$ instead has $t_{\rm rel}\sim4\times10^{16}\,\mathrm{yr}$ and behaves as a <collisionless stellar system>, retaining differences from formation, <galaxy mergers>, and <star formation>. \b[Relaxation erases more memory in clusters than in galaxies], although real <globular clusters> also differ in concentration and evolutionary state, so structural similarity is approximate.
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