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We consider the class of nonlinear evolution equations
that have N-soliton solutions for the dependent variable
u(x,t), where  and f is obtainable by
Hirota's method. The N-soliton solution is decomposed into
a sum  , where, in the limits
 , each  is a 1-soliton solution to
the original governing equation.
During interaction `mass' is conserved for each .
Our formulation of the decomposition does not use
the inverse scattering technique and is similar to
that used forthe KdV equation by Yoneyama (1984b) and Moloney
& Hodnett (1989). Focusing on the case N=2, we discuss
the properties of  and  , and our results are illustrated
by considering an extended KdV equation and the
Sawada-Kotera equation. Also, for each of these equations, the
corresponding `interacting soliton' equations are derived
for general N.
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