  A clutter is \emph{clean} if it has no delta or the blocker of an extended
odd hole minor, and it is \emph{tangled} if its covering number is two and
every element appears in a minimum cover. Clean tangled clutters have been
instrumental in progress towards several open problems on ideal clutters,
including the $\tau=2$ Conjecture.
  Let $\mathcal{C}$ be a clean tangled clutter. It was recently proved that
$\mathcal{C}$ has a fractional packing of value two. Collecting the supports of
all such fractional packings, we obtain what is called the {\it core} of
$\mathcal{C}$. The core is a duplication of the cuboid of a set of $0-1$
points, called the {\it setcore} of $\mathcal{C}$.
  In this paper, we prove three results about the setcore. First, the convex
hull of the setcore is a full-dimensional polytope containing the center point
of the hypercube in its interior. Secondly, this polytope is a simplex if, and
only if, the setcore is the cocycle space of a projective geometry over the
two-element field. Finally, if this polytope is a simplex of dimension more
than three, then $\mathcal{C}$ has the clutter of the lines of the Fano plane
as a minor.
  Our results expose a fascinating interplay between the combinatorics and the
geometry of clean tangled clutters.
