# 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.

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The same variable e2 appears 2 times

( 2023-03-05 11:00:58 +0100 )edit

thanks, corrected!

( 2023-03-05 11:03:07 +0100 )edit

works for me in sage 10.0.beta3

( 2023-03-05 12:54:30 +0100 )edit

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

( 2023-03-06 11:50:35 +0100 )edit

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I confirm the bug in SageMath 9.7, but it has been corrected in SageMath 9.8:

sage: E.<e1,e2,e3> = ExteriorAlgebra(SR)
sage: e1.interior_product(e1)
1
sage: (e1.interior_product(e1)).constant_coefficient()
1


So the solution is to install SageMath 9.8 or to select a SageMath 9.8 kernel on CoCalc.

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