This is a quote from my cryptography notes:
If $h$ is a random function oracle of output length $n$ then also the two KDF constructions:
$K(x) = h( \| x) \ldots \| h([L] \| x)$
$K(x) = h(x \|  ) \ldots \| h(x \| [L])$
yield random function oracles of otput length $L \cdot n$.
They call this property domain separation. What does this property mean? Can it be applied to only this setting or is it more general? What about the proof of this quote, is it inmediate?