TY  - JOUR
AU  - Neil Robertson
AU  - P.D. Seymour
AU  - Robin Thomas
TI  - Permanents, Pfaffian orientations, and even directed circuits
JO  - Annals of mathematics
PY  - 1999
VL  - 150
IS  - 3
UR  - http://geodesic.mathdoc.fr/articles/10.2307/121059/
DO  - 10.2307/121059
ID  - 10_2307_121059
ER  -