Sullivan model of the connected sum of two complex projective planes
= Sullivan model of the connected sum of two complex projective planes
{c}
{title2=$(\Lambda(a_2,b_2,r_3,s_3),dr=ab,\ ds=a^2-b^2)$}
The two quadratic relations form a <regular sequence> in $\mathbb Q[a,b]$, so their <Koszul complex> has only the quotient-ring <cohomology>. Represent the two degree-two classes by rational polynomial forms and choose primitives for the exact relations to obtain a <quasi-isomorphism>. There are no further generators.