  We discuss the hadron--quark crossover accompanied by the formation of Cooper
triples (three-body counterpart of Cooper pairs) by analogy with the
Bose--Einstein condensate to Bardeen--Cooper--Schrieffer crossover in
two-component fermionic systems. Such a crossover is different from a phase
transition, which often involves symmetry breaking. We calculate the in-medium
three-body energy from the three-body $T$-matrix with a phenomenological
three-body force characterizing a bound hadronic state in vacuum. With
increasing density, the hadronic bound-state pole smoothly undergoes a
crossover toward the Cooper triple phase where the in-medium three-body
clusters coexist with the quark Fermi sea. The relation to the quarkyonic
matter model can also be found in a natural manner.
