WHEN WRITING A NODE EQUATION...
AT EACH NODE ONE CAN CHOSE ARBITRARY
DIRECTIONS FOR THE CURRENTS
AND SELECT ANY FORM OF KCL.
WHEN THE CURRENTS ARE REPLACED IN TERMS
OF THE NODE VOLTAGES THE NODE EQUATIONS
THAT RESULT ARE THE SAME OR EQUIVALENT
WHEN WRITING THE NODE EQUATIONS
WRITE THE EQUATION DIRECTLY IN TERMS
OF THE NODE VOLTAGES.
BY DEFAULT USE KCL IN THE FORM
SUM-OF-CURRENTS-LEAVING = 0
THE REFERENCE DIRECTION FOR THE
CURRENTS DOES NOT AFFECT THE NODE
EQUATION