0. Argument

:
 arg(z) <> 0; 0,t
 abs(arg(z)) <> pi/2; t,0
:
 arg(z) > pi/2; t,0;0,t
 arg(z) > 0 and arg(z) < pi/2; t,0;0,t
 arg(z) > -pi/2 and arg(z) < 0; t,0;0,t
 arg(z) < -pi/2; t,0;0,t
