Quick easy question: what is the meaning of the symbol $(\space\space )$. I've seen it now in two papers, one of which is Milgram's Group Representations and the Adams Spectral Sequence, available at [here](https://projecteuclid.org/journals/pacific-journal-of-mathematics/volume-41/issue-1/Group-representations-and-the-Adams-spectral-sequence/pjm/1102968426.full).


On the top of page 170, Milgram writes
$\partial(\space\space) \to S^k\vee S^k\to S^k\to v$


I figure if I knew what was meant by mathematical colloquialism "$\partial(\space \space)$", interpreting this part of the paper would be easy enough, I'm just not sure what it means.


Thanks



what do empty parens symbol mean?
In the case at hand, $v$ is defined as
$$v = \bar{u}(id \times A \times A): E\_{Z\_2} \ltimes D^{r-s} \wedge D^{s-r} \to S$$


The sequence in question, which is described as the 'restriction of $v$ to the boundary', is shorthand for 
$$ \partial(E\_{Z\_2} \ltimes D^{r-s} \wedge D^{s-r}) \stackrel{\pi}{\to} S^k \vee S^k \to S^k \to S^0$$
and the notation $\partial(\ )$ is shorthand for the boundary of the 'obvious thing', the only space that belongs there. The $\pi$ seems to be projection.


I can't comment on the other occurrence, but often in seminars one can write such a notation when trying to save time and/or space on the board, especially if the expression is complicated.


