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## why Maple can not get the simplest answer?

I got two expressions which in essential are the same. But The maple can not give the answer 0 when I did the subtraction btw them. What is the problem here? Or I need to use some other commands? M1 :=subs( {s1^2=mu1*epsilon1*kappa^2+v^2+u^2, s2^2=mu2*epsilon2*kappa^2+v^2+u^2},(1/2)*(-exp(-w*a)*w*epsilon2*exp(-w*xp)*s1*kappa^2-exp(-w*a)*w^2*epsilon2*u^2*exp(-w*xp)*epsilon1+w*v^2*s1*exp(-s2*(a-xp))-w*s1*exp(-s2*(a-xp))*s2^2+exp(-w*a)*w*exp(-s1*xp)*s1^2*s2+w^2*s1*s2*exp(-w*(a-xp))+exp(-w*a)*w^2*epsilon2*u^2*exp(-s1*xp)-s1*exp(-w*(a-xp))*s2*kappa^2+exp(-w*a)*w^2*epsilon2*exp(-s1*xp)*v^2+exp(-w*a)*w*u^2*exp(-w*xp)*epsilon1*s2-exp(-w*a)*w^2*epsilon2*exp(-s1*xp)*s1^2+w^2*v^2*epsilon1*exp(-s2*(a-xp))+w^2*u^2*epsilon1*exp(-s2*(a-xp))-exp(-w*a)*mu1*exp(-s1*xp)*epsilon1*kappa^2*s2*w+exp(-w*a)*mu1*epsilon2*exp(-s1*xp)*epsilon1*kappa^2*w^2-w^2*epsilon1*exp(-s2*(a-xp))*s2^2+w*u^2*s1*exp(-s2*(a-xp))+epsilon1*s2*exp(-w*(a-xp))*w^3-exp(-w*a)*w^2*exp(-w*xp)*s1*s2+exp(-w*a)*exp(-w*xp)*s1*kappa^2*s2-w*epsilon2*u^2*s1*exp(-w*(a-xp))-w^2*epsilon2*v^2*epsilon1*exp(-w*(a-xp))-w^2*epsilon2*u^2*epsilon1*exp(-w*(a-xp))+exp(-w*a)*epsilon2*exp(-w*xp)*s1*w^3-exp(-w*a)*w*u^2*exp(-s1*xp)*s2-exp(-w*a)*w*exp(-s1*xp)*v^2*s2+exp(-w*a)*w*v^2*exp(-w*xp)*epsilon1*s2-exp(-w*a)*w^2*epsilon2*v^2*exp(-w*xp)*epsilon1-w*epsilon2*s1*exp(-w*(a-xp))*v^2+mu2*s1*exp(-s2*(a-xp))*epsilon2*kappa^2*w-w*epsilon1*exp(-w*(a-xp))*s2*kappa^2+mu2*epsilon1*exp(-s2*(a-xp))*epsilon2*kappa^2*w^2)/(kappa^2*(exp(w*a)*w^2*epsilon1*epsilon2+exp(w*a)*w*epsilon1*s2-exp(-w*a)*w^2*epsilon1*epsilon2+w*s2*epsilon1*exp(-w*a)+exp(-w*a)*s1*epsilon2*w-s2*s1*exp(-w*a)+s1*exp(w*a)*epsilon2*w+s1*exp(w*a)*s2)*w)); N1 :=subs( {s1^2=mu1*epsilon1*kappa^2+v^2+u^2, s2^2=mu2*epsilon2*kappa^2+v^2+u^2}, (w*(-epsilon2*w+s2)*(mu1*epsilon1*kappa^2-s1^2+v^2+u^2)*exp(-s1*xp)-w*(w*epsilon1+s1)*(-s2^2+mu2*epsilon2*kappa^2+v^2+u^2)*exp(w*a-s2*(a-xp))-(-epsilon2*w+s2)*(-w^2*s1+w*u^2*epsilon1+w*v^2*epsilon1+s1*kappa^2)*exp(-w*xp)+(s2*kappa^2+epsilon2*w*u^2-w^2*s2+epsilon2*w*v^2)*(w*epsilon1+s1)*exp(w*xp))/(2*kappa^2*w*(w*epsilon1((1+exp(2*w*a))*s2+(-1+exp(2*w*a))*w*epsilon2)+s1*((-1+exp(2*w*a))*s2+(1+exp(2*w*a))*w*s2)))); M1-N1;

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