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Tautomers are isomers that are in equilibrium (e.g. keto-enol tautomerism). Where a single tautomeric form is claimed (explicitly or implicitly free of the other tautomer), disclosure of a different tautomer would not provide an enabling disclosure of the claimed tautomer. In the context of processes utilising a tautomer, an objection of lack of novelty must establish that the compound is in fact in equilibrium with the known compound, and that it was common general knowledge in the particular art that the forms would be in equilibrium.

See Canadian Industries Ltd v Australian Paper Manufacturers Ltd [1983] APO 21, where it was not established that tautomerism would occur.

See Australian Paper Manufacturers Ltd v CIL Inc (1985) 4 IPR 612, where it was not established that the tautomerism was common general knowledge.

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