--- a/src/LazyTensors/lazy_tensor_operations.jl	Mon Oct 19 21:09:11 2020 +0200
+++ b/src/LazyTensors/lazy_tensor_operations.jl	Tue Oct 20 09:07:15 2020 +0200
@@ -147,3 +147,26 @@
 function apply_transpose(llm::LazyLinearMap{T,R,D}, v::AbstractArray{T,R}, I::Vararg{Index,D}) where {T,R,D}
     apply(LazyLinearMap(llm.A, llm.domain_indicies, llm.range_indicies), v, I...)
 end
+
+
+"""
+    IdentityMapping{T,D} <: TensorMapping{T,D,D}
+
+The lazy identity TensorMapping for a given size. Usefull for building up higher dimensional tensor mappings from lower
+dimensional ones through outer products. Also used in the Implementation for InflatedTensorMapping.
+"""
+struct IdentityMapping{T,D} <: TensorMapping{T,D,D}
+    size::NTuple{D,Int}
+end
+export IdentityMapping
+
+IdentityMapping{T}(size::NTuple{D,Int}) where {T,D} = IdentityMapping{T,D}(size)
+IdentityMapping{T}(size::Vararg{Int,D}) where {T,D} = IdentityMapping{T,D}(size)
+IdentityMapping(size::Vararg{Int,D}) where D = IdentityMapping{Float64,D}(size)
+
+range_size(tmi::IdentityMapping) = tmi.size
+domain_size(tmi::IdentityMapping) = tmi.size
+
+apply(tmi::IdentityMapping{T,D}, v::AbstractArray{T,D}, I::Vararg{Any,D}) where {T,D} = v[I...]
+apply_transpose(tmi::IdentityMapping{T,D}, v::AbstractArray{T,D}, I::Vararg{Any,D}) where {T,D} = v[I...]
+

--- a/test/testLazyTensors.jl	Mon Oct 19 21:09:11 2020 +0200
+++ b/test/testLazyTensors.jl	Tue Oct 20 09:07:15 2020 +0200
@@ -281,4 +281,29 @@
 
 end
 
+
+@testset "IdentityMapping" begin
+    @test IdentityMapping{Float64}((4,5)) isa IdentityMapping{T,2} where T
+    @test IdentityMapping{Float64}((4,5)) isa TensorMapping{T,2,2} where T
+    @test IdentityMapping{Float64}((4,5)) == IdentityMapping{Float64}(4,5)
+
+    @test IdentityMapping(3,2) isa IdentityMapping{Float64,2}
+
+    for sz ∈ [(4,5),(3,),(5,6,4)]
+        I = IdentityMapping{Float64}(sz)
+        v = rand(sz...)
+        @test I*v == v
+        @test I'*v == v
+
+        @test range_size(I) == sz
+        @test domain_size(I) == sz
+    end
+
+    I = IdentityMapping{Float64}((4,5))
+    v = rand(4,5)
+    @inferred (I*v)[3,2]
+    @inferred (I'*v)[3,2]
+    @inferred range_size(I)
 end
+
+end