  We consider scalar two-dimensional quantum field theories with the
factorizing S-matrix which has poles in the physical strip. In our previous
work, we introduced the bound state operators and constructed candidate
operators for observables in wedges.
  Under some additional assumptions on the S-matrix, we show that, in order to
obtain their strong commutativity, it is enough to prove the essential
self-adjointness of the sum of the left and right bound state operators. This
essential self-adjointness is shown up to the two-particle component.
