theorem Th3: :: FUZZY_7:20

for a, b, c being Real
for f, g being Function of REAL,REAL st a < b & b < c holds
((f | ].-infty,b.]) +* (g | [.b,+infty.[)) | [.a,c.] = (f | [.a,b.]) +* (g | [.b,c.])