theorem Th9: :: GLIB_011:9

for G1, G2 being non-Dmulti _Graph
for f being PVertexMapping of G1,G2 st f is total & f is one-to-one & f is directed & f is Dcontinuous holds
for v, w being Vertex of G1 holds
( card (G1 .edgesDBetween ({v},{w})) = card (G2 .edgesDBetween ({(f . v)},{(f . w)})) & card (G1 .edgesDBetween ({w},{v})) = card (G2 .edgesDBetween ({(f . w)},{(f . v)})) )