Thinking through an importing event in Three Land:

Working column by column beginning with the smallest blocks,

Fig. 1: Cannot have three Unit Cubes, so trade them for a Long and record zero Unit Cubes left.

Fig. 2: Cannot have four Longs, so trade three of them for a Flat and record one Long left.

Fig. 3: Record the two Flats that are safe and the two Super Cubes that are safe.