TY  - JOUR
AU  - Jiri Adamek
AU  - Vera Trnkova
TI  - Birkhoff's variety theorem with and without free algebras
JO  - Theory and applications of categories
PY  - 2005
SP  - 424
EP  - 450
VL  - 14
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/TAC_2005_14_a17/
LA  - en
ID  - TAC_2005_14_a17
ER  -