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    if (i==3) var filename="topics/discrete_02dif.html";
    
    if (i==4) var filename="topics/nonlinear_equations.html";
    if (i==5) var filename="topics/bisection_method.html";
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    if (i==7) var filename="topics/secant_method.html";
    
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    if (i==9) var filename="topics/gaussian_elimination.html";
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    if (i==22) var filename="topics/simpsons_13rd_rule.html";
    if (i==23) var filename="topics/romberg_method.html";
    if (i==24) var filename="topics/gauss_quadrature.html";
    if (i==25) var filename="topics/improper_integration.html";
    if (i==26) var filename="topics/discrete_data_integration.html";

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