theorem Th69: :: JGRAPH_6:69

for p being Point of (TOP-REAL 2)
for P being non empty compact Subset of (TOP-REAL 2)
for f being Function of (TOP-REAL 2),(TOP-REAL 2) st f = Sq_Circ holds
( (f . p) `2 >= 0 iff p `2 >= 0 )