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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def find_unconstrained_reactions(model):
 """Return list of reactions that are not constrained at all."""

    lower_bound, upper_bound = helpers.find_bounds(model)
    return [rxn for rxn in model.reactions if
            rxn.lower_bound <= lower_bound and
            rxn.upper_bound >= upper_bound]