Copy/Paste the following code to your GroIMP project:
//**********************************************************
/* You will learn:
– the distinction between L-system rules (==>) and
SPO rules (==>>)
– the special character ^ for the root node of the actual graph.
*/

module A extends Sphere(3);

protected void init()
[ Axiom ==> F(20, 4) A; ]

public void runL()
[
A ==> RU(20) F(20, 4) A;
]

public void runSPO()
[
A ==>> ^ RU(20) F(20, 4, 5) A;
]

//**********************************************************