Lloyd Humberstone. Twins in Logic - Identical and Otherwise. FLAP, 7(6):1071-1114, 2020. [doi]
@article{Humberstone20-0, title = {Twins in Logic - Identical and Otherwise}, author = {Lloyd Humberstone}, year = {2020}, url = {http://collegepublications.co.uk/ifcolog/?00042}, researchr = {https://researchr.org/publication/Humberstone20-0}, cites = {0}, citedby = {0}, journal = {FLAP}, volume = {7}, number = {6}, pages = {1071-1114}, }