theorem Th19: :: GLIB_007:19

for G2 being _Graph
for E being set
for G1 being reverseEdgeDirections of G2,E
for v1, v2 being object holds
( ex W1 being Walk of G1 st W1 is_Walk_from v1,v2 iff ex W2 being Walk of G2 st W2 is_Walk_from v1,v2 )