  Gentzen's idea was to extend natural deduction to a system of  arithmetic by the addition of a rule that corresponds to the  principle of complete induction. Consistency would then follow from  the normalization of derivations and the subformula property. By  early 1933, Gentzen realized that this proof strategy would not go  through: the induction rule is schematic and has an infinity of  instances, with no bound on the complexity of the induction formulas. It would be impossible to restrict these formulas in advance, thus no subformula property can hold. After this failure, Gentzen took  verbatim out of his early thesis manuscript the translation from  classical to intuitionistic arithmetic and submitted it as a paper in March 1933, but withdrew the paper after hearing of Gödel's  publication of the result.