--- a/Notes.md	Tue Mar 22 14:33:13 2022 +0100
+++ b/Notes.md	Wed Mar 23 13:09:31 2022 +0100
@@ -146,12 +146,52 @@
  - [ ] Is it ok to have "Constructors" for abstract types which create subtypes? For example a Grids() functions that gives different kind of grids based on input?
  - [ ] Figure out how to treat the borrowing parameters of operators. Include in into the struct? Expose via function dispatched on the operator type and grid?
 
+## Identifiers for regions
+The identifiers (`Upper`, `Lower`, `Interior`) used for region indecies should probabily be included in the grid module. This allows new grid types to come with their own regions.
+
 ## Regions and tensormappings
 - [ ] Use a trait to indicate if a LazyTensor uses indices with regions.
     The default should be that they do NOT.
         - [ ] What to name this trait? Can we call it IndexStyle but not export it to avoid conflicts with Base.IndexStyle?
  - [ ] Figure out repeated application of regioned LazyTensors. Maybe an instance of a tensor mapping needs to know the exact size of the range and domain for this to work?
 
+### Ideas for information sharing functions
+```julia
+using StaticArrays
+
+function regions(op::SecondDerivativeVariable)
+    t = ntuple(i->(Interior(),),range_dim(op))
+    return Base.setindex(t, (Lower(), Interior(), Upper()), derivative_direction(op))
+end
+
+function regionsizes(op::SecondDerivativeVariable)
+    sz = tuple.(range_size(op))
+
+    cl = closuresize(op)
+    return Base.setindex(sz, (cl, n-2cl, cl), derivative_direction(op))
+end
+
+
+g = EquidistantGrid((11,9), (0.,0.), (10.,8.)) # h = 1
+c = evalOn(g, (x,y)->x+y)
+
+D₂ᶜ = SecondDerivativeVariable(g, c, interior_stencil, closure_stencils,1)
+@test regions(D₂ᶜ) == (
+    (Lower(), Interior(), Upper()),
+    (Interior(),),
+)
+@test regionsizes(D₂ᶜ) == ((1,9,1),(9,))
+
+
+D₂ᶜ = SecondDerivativeVariable(g, c, interior_stencil, closure_stencils,2)
+@test regions(D₂ᶜ) == (
+    (Interior(),),
+    (Lower(), Interior(), Upper()),
+)
+@test regionsizes(D₂ᶜ) == ((11,),(1,7,1))
+```
+
+
 ## Boundschecking and dimension checking
 Does it make sense to have boundschecking only in getindex methods?
 This would mean no bounds checking in applys, however any indexing that they do would be boundschecked. The only loss would be readability of errors. But users aren't really supposed to call apply directly anyway.