Question: How do I solve recursive assignment?

I have to solve the following set of equations. But it allways appears the Error "recursive assignment". Has somebody a solution for me? Is there a Problem with the Equations?

DGL1 := m[1]*(D(D(x[1])))(t)+d[1]*((D(x[1]))(t)-(D(x[2]))(t))+c[1]*(x[1](t)-x[2](t))+e^(-0.4e-1*t)*sin(t)+1.5 = 0;
DGL2 := m[2]*(D(D(x[2])))(t)+d[2]*(D(x[2]))(t)+d[1]*(DF[4]-(D(x[2]))(t))+c[2]*(x[2](t)+x[f])+c[1]*(F[4]-x[2](t)) = 0;

init := (D(x[1]))(0) = 0, x[1](0) = 1.5, x[2](0) = 5;
F := dsolve({DGL3, DGL4,init});

Error, recursive assignment

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