Jürgen Schmidt. Algebraic studies of first-order enlargements. Notre Dame Journal of Formal Logic, 22(4):315-343, 1981. [doi]
@article{Schmidt81-1,
title = {Algebraic studies of first-order enlargements},
author = {Jürgen Schmidt},
year = {1981},
doi = {10.1305/ndjfl/1093883513},
url = {http://dx.doi.org/10.1305/ndjfl/1093883513},
researchr = {https://researchr.org/publication/Schmidt81-1},
cites = {0},
citedby = {0},
journal = {Notre Dame Journal of Formal Logic},
volume = {22},
number = {4},
pages = {315-343},
}