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Existence Criteria for Singular Initial Value Problems with Sign Changing Nonlinearities
A general existence theory is presented for initial value problems where our nonlinearity may be singular in its dependent variable and may also change sign.
Birkhoff-Kellogg theorems on invariant directions for multimaps
We establish Birkhoff-Kellogg type theorems on invariant directions for a general class of maps. Our results, in particular, apply to Kakutani, acyclic, O'Neill, approximable, admissible, and script U signCK maps.