Classification of $\mathbb{C}P^2$-multiplicative Hirzebruch genera

The short article [V.M. Buchstaber, E.Yu. Netay, $\mathbb{C}P(2)$-multiplicative Hirzebruch genera and elliptic cohomology, Russian Math. Surveys, 69:4 (2014), 757-759] states results on $\mathbb{C}P(2)$-multiplicative Hirzebruch genera. The aim of the following text is to give a proof of Theorem 3. This proof uses only the technique of functional differential equations.