What does $a \propto i, i \in \{ 1, ..., 10\}=I$ mean?
Does it mean that one takes $i$, e.g. $i=1$ and then constructs more numbers by taking some $k \in \mathbb{R}$ so that $a=ki$? One can take infinite amount of $k$ so one can construct more $a$s than there are $i$s.
Or does the above notation mean the same as $a \in kI$, so that the constant $k$ is the same for all elements $i$?