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Generalized Ordinary Differential Equations in Abstract Spaces and Applications


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right-brace"/> is an equiregulated set. Indeed, by Lemma 1.13, f Subscript k converges uniformly to f 0.

      Since the function f 0 is regulated, its lateral limits exist. Then, for every t 0 element-of left-bracket a comma b right-bracket and every epsilon greater-than 0, there is delta greater-than 0 such that

StartLayout 1st Row 1st Column parallel-to f 0 left-parenthesis t 0 Superscript minus Baseline right-parenthesis minus f 0 left-parenthesis t right-parenthesis parallel-to 2nd Column less-than epsilon comma for t 0 minus delta less-than-or-slanted-equals t less-than t 0 comma 2nd Row 1st Column parallel-to f 0 left-parenthesis t right-parenthesis minus f 0 left-parenthesis t 0 Superscript plus Baseline right-parenthesis parallel-to 2nd Column less-than epsilon comma for t 0 less-than t less-than-or-slanted-equals t 0 plus delta comma EndLayout

      for every t element-of left-bracket a comma b right-bracket.

      But the hypotheses say that we can find n 0 element-of double-struck upper N such that, for n greater-than-or-slanted-equals n 0, we have

parallel-to f Subscript n Baseline left-parenthesis t 0 minus delta right-parenthesis minus f 0 left-parenthesis t 0 minus delta right-parenthesis parallel-to less-than epsilon comma parallel-to f Subscript n Baseline left-parenthesis t 0 right-parenthesis minus f 0 left-parenthesis t 0 right-parenthesis parallel-to less-than epsilon comma parallel-to f Subscript n Baseline left-parenthesis t 0 Superscript plus Baseline right-parenthesis minus f 0 left-parenthesis t 0 Superscript plus Baseline right-parenthesis parallel-to less-than epsilon comma parallel-to f Subscript n Baseline left-parenthesis t 0 plus delta right-parenthesis minus f 0 left-parenthesis t 0 plus delta right-parenthesis parallel-to less-than epsilon and parallel-to f Subscript n Baseline left-parenthesis t 0 Superscript minus Baseline right-parenthesis minus f 0 left-parenthesis t 0 Superscript minus Baseline right-parenthesis parallel-to less-than epsilon period

      When t element-of left-bracket a comma b right-bracket satisfies t 0 minus delta less-than-or-slanted-equals t less-than t 0, we have, for every n greater-than-or-slanted-equals n 0,

parallel-to f Subscript n Baseline left-parenthesis t 0 Superscript minus Baseline right-parenthesis minus f Subscript n Baseline left-parenthesis t right-parenthesis parallel-to less-than-or-slanted-equals parallel-to f Subscript n Baseline left-parenthesis t 0 Superscript minus Baseline right-parenthesis minus f 0 left-parenthesis t 0 Superscript minus Baseline right-parenthesis parallel-to plus parallel-to f 0 left-parenthesis t 0 Superscript minus Baseline right-parenthesis minus f 0 left-parenthesis t right-parenthesis parallel-to plus parallel-to f 0 left-parenthesis t right-parenthesis minus f Subscript n Baseline left-parenthesis t right-parenthesis parallel-to less-than 3 epsilon period parallel-to f Subscript n Baseline left-parenthesis t right-parenthesis minus f Subscript n Baseline left-parenthesis t 0 Superscript plus Baseline right-parenthesis parallel-to less-than-or-slanted-equals parallel-to f Subscript n Baseline left-parenthesis t right-parenthesis minus f 0 left-parenthesis t right-parenthesis parallel-to plus parallel-to f 0 left-parenthesis t right-parenthesis minus f 0 left-parenthesis t 0 Superscript plus Baseline right-parenthesis parallel-to plus parallel-to f Subscript n Baseline left-parenthesis t 0 Superscript plus Baseline right-parenthesis minus f 0 left-parenthesis t 0 Superscript plus Baseline right-parenthesis parallel-to less-than 3 epsilon period

      But this yields the fact that left-brace f Subscript n Baseline right-brace Subscript n element-of double-struck upper N is an equiregulated sequence, and the proof is complete.

      The next lemma guarantees that, if a sequence of functions left-brace f Subscript k Baseline right-brace Subscript k element-of double-struck upper N is bounded by an equiregulated sequence of functions, then left-brace f Subscript k Baseline right-brace Subscript k element-of double-struck upper N is also equiregulated.

      Lemma 1.15: Let be a sequence of functions in . Suppose, for each , the function satisfies

       for every , where for each and the sequence is equiregulated. Then, the sequence is equiregulated.