Star formation triggered by the expansion of an H ii region close to a filament, according to the simulation of Fukuda & Hanawa (2000; their Fig. 1; model C1l’: neutral sound speed 0.3 km s^-1, maximum density on the axis of the filament 2 × 10⁶ cm^-3, exciting star at 0.025 pc of the filament’s axis). The neutral filament appears in grey, the ionized gas in pink; we show what we believe to be the extent of the ionized gas in the plane containing the axis of the filament and the exciting star (black cross) of the H ii region. Schema a) shows the expanding H ii region (age 8.5 × 10⁴ yr) pinching the molecular filament. In schema b), first-generation cores have formed by compression of the neutral material by the ionized gas (age 2.1 × 10⁵ yr). In schema c); second-generation cores have formed due to gravity (age 3.0 × 10⁵ yr). The first- and second-generation cores are separated by 0.1 pc.