Atomic Singular Inner Function
This picture, drawn by Elias Wegert, uses colors to show the phase f/|f| of the complex function
f(z)=5∏k=1exp(z+ωkz−ωk)
where ω is a nontrivial fifth root of unity. This is an ‘atomic singular inner function’. To understand what that means, it helps to start with some complex analysis.