Vertical and horizontal lines are an element of Mondrian's art symbolized harmony between opposites.
D. Teresa Carreno
She was a renowned Venezuelan pianist, singer, conductor, and composer. She composed short piano pieces by the age of 6 and debuted by the age of 8.
I believe that the answer is negative space.
Answer: I've heard of it... somewhere.... Is it good?
Well i'm suggesting it is because you're on the sixth book :)