% 2
 a*a,
 c*a + b*c + a*b,
 e*a + c*e + a*c,
 d*b + b*a + a*d,
 e*d + d*a + a*e,
 f*a + a*f,
 b*b,
 f*b + d*f + b*d,
 e*b + b*e,
 f*c + c*b + b*f,
 c*c,
 d*c + c*d,
 f*e + e*c + c*f,
 d*d,
 f*d + e*f + d*e,
 e*e,
 f*f,
% 3
 b*a*b - a*b*a,
 c*b*c - b*c*b,
 d*a*b - c*d*a - b*a*c + a*c*d,
 d*a*d - a*d*a,
 e*c*d - d*a*c - a*e*c,
 e*c*e - c*e*c,
 e*c*b - d*e*c - c*b*d + b*d*e,
% 4
 c*b*a*c + b*a*c*b + a*c*b*a,
 d*a*c*d + a*d*a*c,
 d*a*c*b + c*b*d*a + b*d*a*c + a*c*b*d,