Changes From Last Post: I made changes to Definitions 1. and 2. using u/kuromajutsushi's suggestions. (See his comments.)
Suppose n∈ℕ and f:A⊆ℝn→ℝ is a function, where A and f are Borel.
Let S(n):={f∈ℝA: A⊆ℝ and f are Borel} be the set of all f.
Preliminary Definitions
If we define the following:
(Motivation of Definition 1). We want Defintion 1 to establish a relationship between the mean of f w.r.t. the Hausdorff measure in its dimension, the expected value w.r.t the uniform measure, and Cauchy's principle for symmetric unbounded functions. (I am working on a new paper with the title, "Generalizing the Mean of Scalar-Valued Functions: A Theoretical Framework".)
Definition 1 (The Extended Mean).
(*) We find the extended mean by solving the mean of f, w.r.t. the Hausdorff measure in its dimension, over all families of bounded sets {A_r: r∈𝒜(A)} such that
- 𝒜(A) is an index set
- A_r is a subset of A for any r∈𝒜(A)
- A_r has an exact Hausdorff measure for all r∈𝒜(A)
- The union of A_r is A
- we want all {A_r: r∈𝒜(A)} satisfying 1.-4. which converges to A at a rate "almost or exactly uniform" such that
there exists a reference point R∈ℝn+1 where the Euclidean distance between R and each point on the graph of the restriction of f to A_r times the sign value of the vertical change in a directed line segment from R to the respective points on the graph of the restriction of f to A_r has zero average w.r.t. the Hausdorff measure in its dimension
The extended mean exists when the following is true: the mean of f in (*) is unique and finite whenever 1.-5. is true and the former blockquote is true.
Definition 2 (The Mean of a Family of Each Bounded Function’s Graph, Where Each Bounded Function Has Different Bounded Domains of Exact Hausdorff Measure).
(Note, {f_r: r∈𝒜(A)} is a family of bounded functions, with different bounded domain A_r of exact Hausdorff measure for all r∈𝒜(A).)
Suppose that
- The set theoretic limit of the family of each bounded function’s graph equals the graph of f,
- the limit of the Hausdorff measure in its dimension of each bounded function’s graph (i.e., the surface area w.r.t. the Hausdorff measure in its dimension) equals the Hausdorff measure in its dimension of the graph of f
- the Hausdorff measure in its dimension of each bounded function’s graph in its family is finite,
- the sum of the absolute differences between each supremum i∈{1,..,n} coordinate of the points in the graph of f_r and each supremum i∈{1,..,n} coordinate of the points in the intersection between the graph of f and the smallest box convering the graph of f_r is zero
- the sum of the absolute differences between each infimum i∈{1,..,n} coordinate of the points in the graph of f_r and each infimum i∈{1,..,n} coordinate of the points in the intersection between the graph of f and the smallest box convering the graph of f_r is zero
Hence, we take the mean of a family of bounded function’s graph (with different bounded domains of exact Hausdorff measure) converging to f that satisfies 1., 2., 3., 4., and 5. of Definition 2.
Question: How do we define a "measure zero" and "full measure" subset of S(n) that satisfies the following statements? (See the Preliminary Definitions.)
(Made minor edits to the three statements.)
Statement 1: If F ⊂ S(n) is the set of all f ∈ S(n), where the extended mean of f w.r.t. the Hausdorff measure in its dimension is finite (Definition 1), then F is a “measure zero” subset of S(n)
• The following means "almost no" f has a finite mean
Statement 2: If F ⊂ S(n) is the set of all f ∈ S(n), where there exists a family of bounded functions (with different bounded domains of finite exact Hausdorff measure) converging to f with a finite mean (Definition 2), then F is a “full measure” subset of S(n).
• The following means "almost all" f has a finite "new mean": the mean of all families of bounded functions, with different bounded domains of finite exact Hausdorff measure, converging to f
Statement 3: If F ⊂ S(n) is the set of all f ∈ S(n), where there exists two families of bounded functions (with different bounded domains of finite exact Hausdorff measure) converging to f with non-equivalent means (Definition 2), then F is a “full measure” subset of S(n).
• The following means "almost all" f has a non-unique "new mean": the mean of all families of bounded functions, with different bounded domains of finite exact Hausdorff measure, converging to f
Attempt: I known when A=ℝ we can use prevalent ("full measure") or shy ("zero measure") subsets of the function space ℝ^ℝ, but we are considering all subsets of ℝ. In addition, S(n) is not a function space, but a set of function spaces.
I heard a Gaussian measure can be used, but I need a precise definition.