The Eisenbud-Green-Harris Conjecture for Defect Two Quadratic Ideals

The Eisenbud-Green-Harris (EGH) conjecture states that a homogeneous ideal in a polynomial ring $K[x_1,\dots ,x_n]$ over a field $K$ that contains a regular sequence $f_1,\dots ,f_n$ with degrees $a_i$, $i=1,\dots ,n$ has the same Hilbert function as a lex-plus-powers ideal containing the powers $x_i^{a_i}$, $i=1,\dots ,n$. In this paper, we discuss a case of the EGH conjecture for homogeneous ideals generated by $n+2$ quadrics containing a regular sequence $f_1,\dots ,f_n$ and give a complete proof for EGH when $n=5$ and $a_1=\cdots =a_5=2$.