theorem Th23: :: ANPROJ_8:27

for p, q, r being Point of (TOP-REAL 3) holds |{p,q,r}| = (((((((p `1) * (q `2)) * (r `3)) - (((p `3) * (q `2)) * (r `1))) - (((p `1) * (q `3)) * (r `2))) + (((p `2) * (q `3)) * (r `1))) - (((p `2) * (q `1)) * (r `3))) + (((p `3) * (q `1)) * (r `2))