A frothy function
in laymans' terms
is a function that maps a rational number
"x" onto an irrational number
and vice versa, with either a finite number of exceptions across
the range of values of x or a finite number of exceptions over a period
of the function.
It's been proven that the cosine function satisfies the first
condition to be a frothy function, that is, it maps a
rational number θ given in degrees onto an irrational
number except for a few points.
The converse has not been
proven so it not known whether a cosine function is a true
frothy function. But if it were, that would be a very interesting thing, because the cosine is at the heart of