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where a is a constant, a 6= 0, ut = ∂u ∂t and so on. The problem of solutions to the Hirota–Ramani equation attracts a lot of attention.In [1, 2] it was demonstrated that this equation is completely integrable by the inverse scattering transform method. The soliton solutions to this equation were obtained in [3] by the Expfunction method. The various hyperbolic, trigonometric and rational function solutions were constructed in [4] by the (G ′ /G)-expansion method. A modification of this method realized in [5] allowed to construct new additional solutions. Other new solutions were obtained by the F -expansion method and an extended version of the Jacobi elliptic functions [6]. The direct rational exponential scheme was applied for constructing the multi-soliton solutions [7]. Simultaneously with the search of new solutions, attention was paid to the study of the properties of this equation. Its Lie symmetries, conservation laws and differential invariants were considered in [8, 9]. The known multi-kink solutions to Eq. (1), including its two-kink solution, may be constructed if the condition ki 6= kj is fulfilled, where ki and kj are the parameters of the components of the solution [7,10]. These components are not one-kink components of a multi-kink solution; the parameters mentioned above are used in the construction of a one-kink solution [11]. In this paper, a two-kink solution to the Hirota– Ramani equation is constructed for the case when k1 = k2. It is done by the partially modified Hirota method [10] that will be completed by new additional conditions. Let us introduce a new dependent variable by means of the equation

Two-kink solution for the Hirota–Ramani equation for degenerated parameters