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
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/AM_1999_150_3_a4/
ID  - AM_1999_150_3_a4
ER  -