  An intensive spectroscopic study was performed for three representative solar
twins (HIP 56948, HIP 79672, and HIP 100963) as well as for the Sun (Moon;
reference standard), with an intention of (1) quantitatively discussing the
relative-to-Sun similarities based on the precisely established differential
parameters and (2) investigating the reason causing the Li abundance
differences despite their similarities. It was concluded that HIP 56948 most
resembles the Sun in every respect including the Li abundance (though not
perfectly similar) among the three and deserves the name of "closest-ever solar
twin", while HIP 79672 and HIP 100963 have somewhat higher effective
temperature and appreciably higher surface Li composition. While there is an
indication of Li being rotation-dependent because the projected rotation in HIP
56948 (and the Sun) is slightly lower than the other two, the rotational
difference alone does not seem to be so large as to efficiently produce the
marked change in Li. Rather, this may be more likely to be attributed (at least
partly) to the slight difference in T_eff via some T_eff-sensitive
Li-controlling mechanism. Since the abundance of beryllium was found to be
essentially solar for all stars irrespective of Li, any physical process
causing the Li diversity should work only on Li without affecting Be.
