It's me again. I am wondering how to compute the preimage of an ideal J⊆B in a ring along a ring homomorphism f:A→B. For simplicity I would be fine with assuming A and B are polynomial rings of finitely many variables over a field. As far as I know, preimages can then be computed algorithmically using Gröbner bases so I think this should be implemented in Sage. However I did not find such a possibility when browsing through the documentation. I hope you can help me (and maybe also point me to where such issues are documented). Thank you!