theorem Th8: :: GOBRD11:8

for s1 being Real
for P1, P2 being Subset of (TOP-REAL 2) st P1 = { |[r,s]| where r, s is Real : s <= s1 } & P2 = { |[r2,s2]| where r2, s2 is Real : s2 > s1 } holds
P1 = P2 `