TY  - JOUR 
T1  - The Feynman propagator for quantum gravity: spin foams, proper time, orientation, causality and timeless-ordering
JO  - Brazilian Journal of Physics
A1  - Oriti, D.
SN  - 0103-9733
UL  - 10.1590/S0103-97332005000300019
VL  - 35 
Y1  - 2005
PB  - Brasil 
ER  -