theorem :: ANPROJ_8:28

for p, q, r, s, t being Point of (TOP-REAL 3) holds ((|{p,q,r}| * |{p,s,t}|) - (|{p,q,s}| * |{p,r,t}|)) + (|{p,q,t}| * |{p,r,s}|) = 0