src/HOL/Hahn_Banach/Function_Order.thy
changeset 61879 e4f9d8f094fe
parent 61540 f92bf6674699
equal deleted inserted replaced
61878:fa4dbb82732f 61879:e4f9d8f094fe
     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 ::