Let say we have a set k $\subset R$
K = [a,b) for convenient k = $[0,\infty)$,
How do we represent some function such as $f:K \to R$
can we represent f:k like y= ..... ??
or we can only represent the some function f:k to a subset.
sorry for little confuse of the question. but i'm also confuse that my question is valid or not