Also, there may be hadrons which lie outside the quark model.

This offered a severe problem for the quark model.

Results from this accelerator helped to lay the experimental foundations of the quark model.

Does this mean that the quark model will soon be complete?

And do you absolutely believe the quark model?

In the following years a number of suggestions appeared for extending the quark model to six quarks.

It is now understood as a result of the quark model.

This scheme is now explained by the quark model.

Thus, isospin was introduced as a concept well before the development in the 1960s of the quark model which provides our modern understanding.

As a result, all assignments outside the quark model are tentative.