  We prove a tangle-tree theorem and a tangle duality theorem for abstract
separation systems $\vec S$ that are submodular in the structural sense that,
for every pair of oriented separations, $\vec S$ contains either their meet or
their join defined in some universe $\vec U$ of separations containing $\vec
S$.
  This holds, and is widely used, if $\vec U$ comes with a submodular order
function and $\vec S$ consists of all its separations up to some fixed order.
Our result is that for the proofs of these two theorems, which are central to
abstract tangle theory, it suffices to assume the above structural consequence
for $\vec S$, and no order function is needed.
