  A Robinson space is a dissimilarity space $(X,d)$ (i.e., a set $X$ of size
$n$ and a dissimilarity $d$ on $X$) for which there exists a total order $<$ on
$X$ such that $x<y<z$ implies that $d(x,z)\ge \max\{ d(x,y), d(y,z)\}$.
Recognizing if a dissimilarity space is Robinson has numerous applications in
seriation and classification. An mmodule of $(X,d)$ (generalizing the notion of
a module in graph theory) is a subset $M$ of $X$ which is not distinguishable
from the outside of $M$, i.e., the distance from any point of $X\setminus M$ to
all points of $M$ is the same. If $p$ is any point of $X$, then $\{ p\}$ and
the maximal by inclusion mmodules of $(X,d)$ not containing $p$ define a
partition of $X$, called the copoint partition. In this paper, we investigate
the structure of mmodules in Robinson spaces and use it and the copoint
partition to design a simple and practical divide-and-conquer algorithm for
recognition of Robinson spaces in optimal $O(n^2)$ time.
