Hello,

I am calculating a Bose-Hubbard model with a square term in its Hamiltonian:@@\widehat{H}=\sum_j{\left( \widehat{a}_{j}^{\dagger 2}+\widehat{a}_{j}^{2} \right)}@@ where @@\widehat{a}_{j}@@ is the annihilation operator of boson.

When I used code

```
ampo += 1, "Adag", i, "Adag", i;
ampo += 1, "A", i, "A", i;
```

with lattice class 'Boson' and run the code, the terminal gave feedback telling

```
I = (dim=5|id=964|"l=1,Link") <Out>
1: 3 QN()
2: 1 QN({"Nb",-1})
3: 1 QN({"Nb",1})
Q = QN({"Nb",-2})
From line 683, file index.cc
Index does not contain given QN block.
Aborted (core dumped)
```

which I also met when I used code like

```
ampo += 1, "S+", i, "S+", i;
ampo += 1, "S-", i, "S-", i;
```

in the spin system. I think I have to prime the operator to make them contract? But I have no idea how to do it in autoMPO class.

Could you please tell me how can I construct a Hamiltonian containing a term like this? Thank you.