  Differential algebra approaches to structural identifiability analysis of a
dynamic system model in many instances heavily depend upon Ritt's
pseudodivision at an early step in analysis. The pseudodivision algorithm is
used to find the characteristic set, of which a subset, the input-output
equations, is used for identifiability analysis. A simpler algorithm is
proposed for this step, using Gr\"obner Bases, along with a proof of the method
that includes a reduced upper bound on derivative requirements. Efficacy of the
new algorithm is illustrated with two biosystem model examples.
