Core idea

Let P=(G,R)P=(G,R) be a , with GG a subgroup of the units of the ambient RR. Its associated has multiplicative group GG and null set

NP={igiN[G]:0igi in R}.N_P= \left\{\sum_i g_i\in\mathbb N[G]: 0\in\mathop{\boxplus}_i g_i\text{ in }R\right\}.

The construction uses the ambient hypersum in RR, not only binary partial sums that remain visible in G{0}G\cup\{0\}. It therefore records null relations even when every attempted parenthesization passes through elements outside the selected coefficient set.

For an ordinary ambient ring this specializes to the . Taking G=R×G=R^\times with RR a hyperfield specializes to the .

References

Matthew Baker and Nathan Bowler, “Matroids over partial hyperstructures,” Advances in Mathematics 343 (2019), 821–863. arXiv:1709.09707.