cleari()
showAxes()
setBackground(white)
val pic1 = Picture.rectangle(50, 50)
val pic2 = Picture.rectangle(25, 25)
val pics = picStackCentered(pic1, pic2)
val pic4 = Picture.rectangle(100, 100)
val col = picColCentered(pics, Picture.vgap(30), pic4)
drawCentered(col)