Hello everyone, I have a problem with 4 degrees of freedom, 2 of which are superfluous. My goal is to derive the equations of motion. I have derived the equations connecting the superfluous DoFs with the independent ones, however they are nonlinear and interlaced, which means that I cannot solve the constraint equations to derive expressions for each variable in order to make substitutions. I know that in larger scale problems where it is difficult to substitute the superfluous DOFs we use Lagrange multipliers. However, my books only mention cases of linear constraints and I cannot think of a way to use Lagrange multipliers with the interlaced equations. Does anyone have a pointer?