theorem Th58: :: GLIB_013:58

for G1, G2 being _Graph
for F being PGraphMapping of G1,G2 st F is onto & F is semi-Dcontinuous holds
( G2 .supInDegree() c= G1 .supInDegree() & G2 .supOutDegree() c= G1 .supOutDegree() )