Here by "QN" degeneracy I mean that two Index-QN pair defined in an IQIndex have the same QN (quantum number). For example, the following two pairs are degenerate :

```
Index(nameint("pzm101",n),1,Site),QN({0,-1},{2,1},{0,1},{0,1})
Index(nameint("pzm020",n),1,Site),QN({0,-1},{2,1},{0,1},{0,1})
```

if such degeneracy appears in the definition of IQIndex, than "segmentation fault" might happen. I seems we can redefine a Index-QN pair with two sector:

```
Index(nameint("pzm***",n),2,Site),QN({0,-1},{2,1},{0,1},{0,1})
```

But it may have problems when we try to define operators. On the other hand, QN only receive at most 4 slots, I can no longer add an additional quantum number to distinguish these two states.

Thank you.

For your last question, I think maybe you can edit the qn.h to allow more QNs.

There are code as follows:

explicit

QN(qn_t q0);

QN(qn_t q0,

qn_t q1);

QN(qn_t q0,

qn_t q1,

qn_t q2);

QN(qn_t q0,

qn_t q1,

qn_t q2,

qn_t q3);

you may just try to add a similiar one:

QN(qn_t q0,

qn_t q1,

qn_t q2,

qn_t q3,

qn_t q4);

Would that work?

Zhiyu