I have the sentence at the moment
Notice that for all $c \in \mathbf{C}$ such that $W(cx) = |c|^{2} Wx$.
which I do not like.
I mean to say that for all $c \in \mathbf C$ the equation is true.
Probably simply
Notice for all $c \in \mathbf C, W(cx) = |c|^{2} Wx.$
How can you formulate the sentence about the distribution equation better, when it should stay as a notification only?
Before I have defined this:
$W: L^{2}(\mathbf R) \to L^{2}(\mathbf R \times \mathbf R)$
My offer would be