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9 begin |
9 begin |
10 |
10 |
11 subsection \<open>The graph of a function\<close> |
11 subsection \<open>The graph of a function\<close> |
12 |
12 |
13 text \<open> |
13 text \<open> |
14 We define the \<^emph>\<open>graph\<close> of a (real) function \<open>f\<close> with |
14 We define the \<^emph>\<open>graph\<close> of a (real) function \<open>f\<close> with domain \<open>F\<close> as the set |
15 domain \<open>F\<close> as the set |
|
16 \begin{center} |
15 \begin{center} |
17 \<open>{(x, f x). x \<in> F}\<close> |
16 \<open>{(x, f x). x \<in> F}\<close> |
18 \end{center} |
17 \end{center} |
19 So we are modeling partial functions by specifying the domain and |
18 So we are modeling partial functions by specifying the domain and the |
20 the mapping function. We use the term ``function'' also for its |
19 mapping function. We use the term ``function'' also for its graph. |
21 graph. |
|
22 \<close> |
20 \<close> |
23 |
21 |
24 type_synonym 'a graph = "('a \<times> real) set" |
22 type_synonym 'a graph = "('a \<times> real) set" |
25 |
23 |
26 definition graph :: "'a set \<Rightarrow> ('a \<Rightarrow> real) \<Rightarrow> 'a graph" |
24 definition graph :: "'a set \<Rightarrow> ('a \<Rightarrow> real) \<Rightarrow> 'a graph" |
39 |
37 |
40 |
38 |
41 subsection \<open>Functions ordered by domain extension\<close> |
39 subsection \<open>Functions ordered by domain extension\<close> |
42 |
40 |
43 text \<open> |
41 text \<open> |
44 A function \<open>h'\<close> is an extension of \<open>h\<close>, iff the graph of |
42 A function \<open>h'\<close> is an extension of \<open>h\<close>, iff the graph of \<open>h\<close> is a subset of |
45 \<open>h\<close> is a subset of the graph of \<open>h'\<close>. |
43 the graph of \<open>h'\<close>. |
46 \<close> |
44 \<close> |
47 |
45 |
48 lemma graph_extI: |
46 lemma graph_extI: |
49 "(\<And>x. x \<in> H \<Longrightarrow> h x = h' x) \<Longrightarrow> H \<subseteq> H' |
47 "(\<And>x. x \<in> H \<Longrightarrow> h x = h' x) \<Longrightarrow> H \<subseteq> H' |
50 \<Longrightarrow> graph H h \<subseteq> graph H' h'" |
48 \<Longrightarrow> graph H h \<subseteq> graph H' h'" |
91 |
89 |
92 |
90 |
93 subsection \<open>Norm-preserving extensions of a function\<close> |
91 subsection \<open>Norm-preserving extensions of a function\<close> |
94 |
92 |
95 text \<open> |
93 text \<open> |
96 Given a linear form \<open>f\<close> on the space \<open>F\<close> and a seminorm \<open>p\<close> on \<open>E\<close>. The |
94 Given a linear form \<open>f\<close> on the space \<open>F\<close> and a seminorm \<open>p\<close> on \<open>E\<close>. The set |
97 set of all linear extensions of \<open>f\<close>, to superspaces \<open>H\<close> of \<open>F\<close>, which are |
95 of all linear extensions of \<open>f\<close>, to superspaces \<open>H\<close> of \<open>F\<close>, which are |
98 bounded by \<open>p\<close>, is defined as follows. |
96 bounded by \<open>p\<close>, is defined as follows. |
99 \<close> |
97 \<close> |
100 |
98 |
101 definition |
99 definition |
102 norm_pres_extensions :: |
100 norm_pres_extensions :: |