On the Perturbation of a Periodic Solution when the Variational System has Non-Trivial Periodic Solutions
D. Lewis
Indiana University Mathematics Journal
1955
text
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10.1512/iumj.1955.4.54031
10.1512/iumj.1955.4.54031
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Indiana Univ. Math. J. 4 (1955) 795 - 815
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