Mathematical functions are all around us. We may not realize it but they are there! Check it out on the pictures below.

A blade of light, selected by the venetian blinds of my living room window, draws a curved, complicated, multiple-valued function on the semi-transparent orange curtains. Maybe the curve below is even more fascinating:

And this is only what we observe macroscopically... By examining the boundary of the illuminated regions, we would detect the diffraction pattern of the blind, which would be described by an even more fascinating function. But that is matter for a separate post...