@article{GDZPPN001261193, title = {Permutability of normal extensions of a semilattice.}, journal = {Semigroup forum}, volume = {43}, year = {1991}, pages = {151-162}, zbl = {0737.20031}, url = {http://dml.mathdoc.fr/item/GDZPPN001261193} }
Piochi, B. Permutability of normal extensions of a semilattice.. Semigroup forum, Tome 43 (1991) pp. 151-162. http://gdmltest.u-ga.fr/item/GDZPPN001261193/