[TU Gifted Math#10]

3.1) 3-degree Schur inequality
3.2) $\leftrightarrow \sum_{cyc} (a-b)^2\ge 0$
3.3) $\leftrightarrow \sum_{cyc}a^5+2abc\sum_{cyc}a^2\ge \sum_{sym}a^4b+abc\sum_{cyc}ab$ then using 5-degree Schur inequality