Z}})$ be the homology classes of the exceptional divisors with self-intersection numbers $E_i\cdot E_i=-1$. Then, by  with $2\chi+3\sigma=7$, $${{\mathcal C}}= \left\{c={{\mathrm{PD}}}(nL-n_1E_1-n_2E_2)\,\bigg|\,
\begin{array}{l}
n,\,n_1,\,n_2\mbox{ are odd},\\
n^2-n_1^2-n_2^2=7
\end{array}\right\}.$$ The set ${{\mathcal E}}$ of all classes $E\in H_2(M;{{\mathbb Z}})$ satisfying $E\cdot E=-1$ is given by $${{\mathcal E}}= \{E=mL+m_1E_1+m_2E_2\,|\,m^2-m_1^2-m_2^2=-1\}.$$ A theorem of Li–Liu [@LL1; @LL2] asserts the following for every $a\in H^2(M;{{\mathbb R}})$.

[**(I)**]{} [*${{\mathcal C}}_{{\mathrm{symp}}}={{\mathcal C}}$.*]{}

[**(II)**]{} [*The diffeomorphism group acts transitively on ${{\mathcal C}}_{{\mathrm{symp}}}$.*]{}

[**(III)**]{} [*${{\mathcal S}}_a\ne\emptyset$ if and only if $a^2>0$ and ${\langle a, E\rangle}\ne 0$ for every $E\in{{\mathcal E}}$.*]{}

[**(IV)**]{} [*${{\mathcal S}}_a\ne\emptyset\implies\#{{\mathcal C}}_a=1$.*]{}

[**(V)**]{} [*If ${{\omega}}_0,{{\omega}}_1$ are symplectic forms on $M$, then there exists a diffeomorphism ${{\varphi}}$ of $M$ such that ${{\omega}}_0$ and ${{\varphi}}^*{{\omega}}_1$ can be joined by a path of symplectic forms.*]{}

Assuming Seiberg–Witten theory, assertion (VI) below is Lemma 3.11 in Karshon–Kessler–Pinsonnault [@KKP] and (VII) is Theorem 1.1 in McDuff [@MCDUFF5].

[**(VI)**]{} [*Two symplectic forms ${{\omega}}_0,{{\omega}}_1$ on $M$ have the same first Chern class if and only if there exists a diffeomorphism ${{\varphi}}$ of $M$, inducing the identity on homology, such that ${{\omega}}_0$ and ${{\varphi}}^*{{\omega}}_1$ can be joined by a path of symplectic forms.*]{}

[**(VII)**]{} [*Two symplectic forms ${{\omega}}_0,{{\omega}}_1$ on $M$ represent the same cohomology class if 