Renyi, Ma, A Remark on the Symplectic Blow-up in Dimension 4, Acta Mathematica Sinica, New Series Chinese Journal of Mathematics, 12(4), 1996, pp. 379-384
In this note, we prove that the symplectic blow-up or blow-down in the dimension 4 is rigid, i.e. the symplectic area of the divisor does not exceed the symplectic radius of the neighbourhood on which we do the blow-up or blow-down.