# problem with constant_coefficient of a form of ExteriorAlgebra

Hi,
I have a problem with ExteriorAlgebra and I do not understand where I am wrong. Let's define an ExteriorAlgebra `E`

with some generators:

```
E.<e1,e2,e3> = ExteriorAlgebra(SR)
```

Take for example `e1`

and compute

```
e1.interior_product(e1)
```

which gives `1`

, correctly. If I instead compute

```
(e1.interior_product(e1)).constant_coefficient()
```

this gives `0`

!

It worked correctly until time ago, this behaviour only appear now: so probably I'm missing something that changed recently. I'm using SageMath version 9.7 on CoCalc.

Thanks in advance!

The same variable e2 appears 2 times

thanks, corrected!

works for me in sage 10.0.beta3

@FrédéricC: thanks for pointing this; actually it works in Sage 9.8 as well (cf. answer below).