>>87

 a^(2/3) = A,b^(2/3) = B,c^(2/3) = C とおくと、

 aa+bb+cc - 2(ab+bc+ca) + 2abc+1
 ≧ A^3 + B^3 + C^3 - 2{AB(A+B) +BC(B+C) +CA(C+A)} + 3ABC
 = 兩3(A,B,C)     >>513
 = F_1(A,B,C)
 ≧ 0,