  We discuss a GC formation scenario in which the first generation (1G) of
single asymptotic giant branch (AGB) stars and intermediate-mass close binaries
(IMCBs) eject gas, from which the second generation (2G) of stars can be
formed. The two key parameters in the scenario are the fractions of binary
stars (f_b) and the slopes (alpha) of the stellar initial mass functions (IMFs)
for 1G stars. Principle results derived by analytic and one-zone models of GC
formation are as follows. The mass fraction of 2G stars (f_2g) can be higher
than ~0.4 for alpha < 1.8 and is not so dependent on f_b. The ratio of the
initial mass of a GC to the present-day mass (M_gc) ranges from 2 to 7
depending on alpha for 0.5 < f_b <0.9. The differences in [Na/Fe] between 1G
and 2G stars can be as large as 0.7 for a wide range of model parameters. The
Li abundances of 2G stars can be as high as those of 1G even if the pristine
gas from IMCBs is assumed to be Li-free. Formation histories of 2G stars show
at least two peaks owing to two peaks in the total ejection rate of gas from
IMCB populations. The observed correlation between f_2g and M_gc can be due to
alpha depending on M_gc. The hypothetical long duration of 2G formation (~ 10^8
yr) is possible, because massive star formation can be suppressed through
frequent dynamical interaction between 1G stars and gas clouds.
