Generalized Ordinary Differential Equations in Abstract Spaces and Applications. Группа авторов

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Generalized Ordinary Differential Equations in Abstract Spaces and Applications - Группа авторов

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target="_blank" rel="nofollow" href="#fb3_img_img_839ae9fb-26bc-5324-bd19-eeb277c6544a.png" alt="StartAbsoluteValue d EndAbsoluteValue"/>. Since script 풜 is equiregulated, there is delta 1 element-of left-parenthesis 0 comma b minus a right-bracket such that parallel-to f left-parenthesis t right-parenthesis minus f left-parenthesis a Superscript plus Baseline right-parenthesis parallel-to less-than-or-slanted-equals StartFraction epsilon Over 2 EndFraction comma for every f element-of script 풜 and t element-of left-parenthesis a comma a plus delta 1 right-parenthesis. Let a 1 equals a plus delta 1 and a equals t 0 less-than t 1 equals a 1. Thus, for left-bracket t comma t Superscript prime Baseline right-bracket subset-of left-parenthesis a comma a 1 right-parenthesis and f element-of script 풜, we have

parallel-to f left-parenthesis t right-parenthesis minus f left-parenthesis t Superscript prime Baseline right-parenthesis parallel-to less-than-or-slanted-equals parallel-to f left-parenthesis t right-parenthesis minus f left-parenthesis a Superscript plus Baseline right-parenthesis parallel-to plus parallel-to f left-parenthesis t Superscript prime Baseline right-parenthesis minus f left-parenthesis a Superscript plus Baseline right-parenthesis parallel-to less-than-or-slanted-equals epsilon period

      Hence, a 1 element-of upper B.

      Let c overTilde be the supremum of the set upper B. Since f element-of script í’œ, f is regulated. Thus, there exists delta greater-than 0 such that parallel-to f left-parenthesis c overTilde Superscript minus Baseline right-parenthesis minus f left-parenthesis t right-parenthesis parallel-to less-than-or-slanted-equals StartFraction epsilon Over 2 EndFraction for every f element-of script í’œ and t element-of left-parenthesis c overTilde minus delta comma c overTilde right-parenthesis intersection left-bracket a comma b right-bracket. Take c element-of upper B intersection left-parenthesis c overTilde minus delta comma c overTilde right-parenthesis and a division d double-prime element-of upper D Subscript left-bracket a comma c right-bracket, say, d double-prime colon a equals t 0 less-than t 1 less-than midline-horizontal-ellipsis less-than t Subscript StartAbsoluteValue d Sub Superscript double-prime Subscript EndAbsoluteValue Baseline equals c, such that (1.1) holds with StartAbsoluteValue d double-prime EndAbsoluteValue instead of StartAbsoluteValue d EndAbsoluteValue. Denote t Subscript StartAbsoluteValue d double-prime EndAbsoluteValue plus 1 Baseline equals c overTilde. Then, for left-bracket t comma t Superscript prime Baseline right-bracket subset-of left-parenthesis t Subscript StartAbsoluteValue d Sub Superscript double-prime Subscript EndAbsoluteValue Baseline comma t Subscript StartAbsoluteValue d Sub Superscript double-prime Subscript EndAbsoluteValue plus 1 Baseline right-parenthesis and f element-of script í’œ, we have

parallel-to f left-parenthesis t right-parenthesis minus f left-parenthesis t Superscript prime Baseline right-parenthesis parallel-to less-than-or-slanted-equals parallel-to f left-parenthesis t right-parenthesis minus f left-parenthesis c overTilde Superscript minus Baseline right-parenthesis parallel-to plus parallel-to f left-parenthesis t Superscript prime Baseline right-parenthesis minus f left-parenthesis c overTilde Superscript minus Baseline right-parenthesis parallel-to less-than-or-slanted-equals epsilon comma

      which implies c overTilde element-of upper B. Thus, we have two possibilities: either c overTilde equals b or c overTilde less-than b. In the first case, the proof is finished. In the second case, one can use a similar argument as the one we used before in order to find e element-of left-parenthesis c overTilde comma b right-bracket such that e element-of upper B, and this contradicts the fact that c overTilde equals sup upper B. Thus, c overTilde equals b, and we finish the proof of the sufficient condition.

      left-parenthesis left double arrow right-parenthesis Now, we prove the necessary condition. Given epsilon greater-than 0, there exists a division d prime element-of upper D Subscript left-bracket a comma b right-bracket, say, d prime colon a equals t 0 less-than t 1 less-than midline-horizontal-ellipsis less-than t Subscript StartAbsoluteValue d Sub Superscript prime Subscript EndAbsoluteValue Baseline equals b such that the inequality (1.1) is fulfilled, for every f element-of script í’œ and every left-bracket t comma t Superscript prime Baseline right-bracket subset-of left-parenthesis t Subscript j minus 1 Baseline comma t Subscript j Baseline right-parenthesis, with j equals 1 comma 2 comma ellipsis comma StartAbsoluteValue d prime EndAbsoluteValue. Then, for every j equals 1 comma 2 comma ellipsis comma StartAbsoluteValue 
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