Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2021/iii/paper-146/2/b/solution

Take the Hirzebruch surface with its standard toric Kähler structure. Let be its negative section of a Hirzebruch surface, and let represent the fiber class of a Hirzebruch surface and meet once. Thus
The preceding smoothing produces an embedded symplectic in class .
Suppose a compatible almost complex structure made all three surfaces almost complex. Since and are distinct, Positive intersection of J-holomorphic curves would imply . Homologically, however,
a contradiction. Hence this example cannot admit such a simultaneous compatible structure.

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