User blog comment:Syst3ms/Using cellular automata to generate a potentially uncomputable function/@comment-35470197-20190205001808

Does \(Q\) mean \(\mathbb{Q}\), i.e. the set of rational numbers? When you want to write a map \(f\) from a set A to a set B, then you are supposed to write \(f \colon A \to B\), but not \(f \colon A \mapsto B\). On the other hand, when you want to a map \(f\) which assigns an element a to a corresponding element \(f(a)\), then you are supposed to write \(f \colon a \mapsto f(a)\). For example, the function \(f(x) = x^2\) is expressed as \(f \colon \mathbb{N} \to \mathbb{N}, \ x \mapsto x^2\).