  Flavour-exotic tetraquark mesons, by definition bound states of two quarks
and two antiquarks of four mutually different quark flavours, are, for given
Lorentz features, subject to two incompatible constraints: On the one hand,
within quantum chromodynamics a formation of compact tetraquark states is most
easily envisaged by merging two colour-antisymmetric two-quark clusters, a
diquark and an antidiquark. This path, however, leads to merely a single
tetraquark state of chosen Lorentz characteristics. On the other hand, in the
limit of the number of colour degrees of freedom growing beyond bounds,
internal consistency at leading order calls for the presence of (at least) two
of such tetraquark states of identical quark-flavour composition. The failure
of attempts to reconcile these two contradictory insights suggests the
nonexistence of compact flavour-exotic tetraquark mesons.
