G. P. Monro. The Concept of Multiset. Math. Log. Q., 33(2):171-178, 1987. [doi]
@article{Monro87, title = {The Concept of Multiset}, author = {G. P. Monro}, year = {1987}, doi = {10.1002/malq.19870330212}, url = {http://dx.doi.org/10.1002/malq.19870330212}, researchr = {https://researchr.org/publication/Monro87}, cites = {0}, citedby = {0}, journal = {Math. Log. Q.}, volume = {33}, number = {2}, pages = {171-178}, }