diff --git a/docs/make.jl b/docs/make.jl
index 5a6ec58..d785c95 100644
--- a/docs/make.jl
+++ b/docs/make.jl
@@ -13,6 +13,12 @@ makedocs(;
     ),
     pages=[
         "Home" => "index.md",
+        "Layers" => [
+            "Transformation" => "transformation.md",
+            "Arithmetic" => "arithmetic.md",
+            "Aggregation" => "aggregation.md",
+            "Comparison" => "comparison.md",
+        ],
     ],
 )
 
diff --git a/docs/src/aggregation.md b/docs/src/aggregation.md
new file mode 100644
index 0000000..e69de29
diff --git a/docs/src/arithmetic.md b/docs/src/arithmetic.md
new file mode 100644
index 0000000..e69de29
diff --git a/docs/src/comparison.md b/docs/src/comparison.md
new file mode 100644
index 0000000..e69de29
diff --git a/docs/src/transformation.md b/docs/src/transformation.md
new file mode 100644
index 0000000..e69de29
diff --git a/src/CompositionalNetworks.jl b/src/CompositionalNetworks.jl
index f38e988..89f8f1f 100644
--- a/src/CompositionalNetworks.jl
+++ b/src/CompositionalNetworks.jl
@@ -1,5 +1,15 @@
 module CompositionalNetworks
 
-# Write your package code here.
+# Exports utilities
+export lazy, lazy_param
+
+# Include utils
+include("utils.jl")
+
+# Includes layers
+include("transformation.jl")
+include("arithmetic.jl")
+include("aggregation.jl")
+include("comparison.jl")
 
 end
diff --git a/src/aggregation.jl b/src/aggregation.jl
new file mode 100644
index 0000000..4b76070
--- /dev/null
+++ b/src/aggregation.jl
@@ -0,0 +1,11 @@
+"""
+    _sum(x::V)
+Aggregate through `+` a vector into a single scalar.
+"""
+_sum(x::V) where {T <: Number, V <: AbstractVector{T}} = reduce(+, x)
+
+"""
+    _count_positive(x::V)
+Count the number of strictly positive elements of `x`.
+"""
+_count_positive(x::V) where {T <: Number, V <: AbstractVector{T}} = count(y -> y > 0.0, x)
\ No newline at end of file
diff --git a/src/arithmetic.jl b/src/arithmetic.jl
new file mode 100644
index 0000000..6d6ffc6
--- /dev/null
+++ b/src/arithmetic.jl
@@ -0,0 +1,11 @@
+"""
+    _sum(x::W) where {T <: Number, V <: AbstractVector{T}, W <: AbstractVector{V}}
+    _prod(x::W) where {T <: Number, V <: AbstractVector{T}, W <: AbstractVector{V}}
+Reduce `k = length(x)` vectors through sum/product to a single vector.
+"""
+function _sum(x::W) where {T <: Number, V <: AbstractVector{T}, W <: AbstractVector{V}}
+    return reduce((y, z) -> y .+ z, x)
+end
+function _prod(x::W) where {T <: Number, V <: AbstractVector{T}, W <: AbstractVector{V}}
+    return reduce((y, z) -> y .* z, x)
+end
diff --git a/src/comparison.jl b/src/comparison.jl
new file mode 100644
index 0000000..5f38c80
--- /dev/null
+++ b/src/comparison.jl
@@ -0,0 +1,48 @@
+# doc in transformation.jl
+_identity(x::T) where T <: Number = identity(x)
+
+"""
+    _abs_diff_val_param(x::T, param::T)
+Return the absolute difference between `x` and `param`.
+"""
+_abs_diff_val_param(x::T, param::T) where T <: Number = abs(x - param)
+
+"""
+    _val_minus_param(x::T, param::T)
+    _param_minus_val(x::T, param::T)
+Return the difference `x - param` (resp. `param - x`) if positive, `0.0` otherwise.
+"""
+_val_minus_param(x::T, param::T) where T <: Number = max(0.0, x - param)
+_param_minus_val(x::T, param::T) where T <: Number = max(0.0, param - x)
+
+"""
+    _euclidian_param(x::T, param::T, dom_size::T2)
+    _euclidian(x::T, dom_size::T2)
+Compute an euclidian norm , possibly weigthed by `param`, on a scalar.
+"""
+function _euclidian_param(x::T, param::T, dom_size::T2) where {T <: Number, T2 <: Number}
+    return x == param ? 0.0 : (1.0 + abs(x - param) \ dom_size)
+end
+function _euclidian(x::T, dom_size::T2) where {T <: Number, T2 <: Number}
+    return _euclidian_param(x, zero(T), dom_size)
+end
+
+"""
+    _abs_diff_val_vars(x::T, vars::V)
+Return the absolute difference between `x` and the number of variables.
+"""
+function _abs_diff_val_vars(x::T, vars::V) where {T <: Number, V <: AbstractVector{T}}
+    return abs(x - length(vars))
+end
+
+"""
+    _val_minus_vars(x::T, vars::V)
+    _vars_minus_val(x::T, vars::V)
+Return the difference `x - length(vars)` (resp. `length(vars) - x`) if positive, `0.0` otherwise.
+"""
+function _val_minus_vars(x::T, vars::V) where {T <: Number, V <: AbstractVector{T}}
+    return _val_minus_param(x, length(vars))
+end
+function _vars_minus_val(x::T, vars::V) where {T <: Number, V <: AbstractVector{T}}
+    return _param_minus_val(x, length(vars))
+end
diff --git a/src/transformation.jl b/src/transformation.jl
new file mode 100644
index 0000000..e6050ba
--- /dev/null
+++ b/src/transformation.jl
@@ -0,0 +1,115 @@
+"""
+    _identity(x::V) where {T <: Number,V <: AbstractVector{T}}
+    _identity(x::T) where T <: Number = identity(x)
+Identity function. Already defined in Julia as `identity`, specialized for vectors and scalars.
+"""
+_identity(x::V) where {T <: Number,V <: AbstractVector{T}} = identity(x)
+
+"""
+    _count_eq(i::Int, x::V)
+    _count_eq_right(i::Int, x::V)
+    _count_eq_left(i::Int, x::V)
+Count the number of elements equal to `x[i]` (optionally to the right/left of `x[i]`). Extended method to vector `x::V` are generated.
+"""
+function _count_eq(i::Int, x::V) where {T <: Number,V <: AbstractVector{T}}
+    return count(y -> x[i] == y, x) - 1
+end
+function _count_eq_right(i::Int, x::V) where {T <: Number,V <: AbstractVector{T}}
+    return _count_eq(1, @view x[i:end])
+end
+function _count_eq_left(i::Int, x::V) where {T <: Number,V <: AbstractVector{T}}
+    return _count_eq(i, @view x[1:i])
+end
+# Generating vetorized versions
+lazy(_count_eq, _count_eq_left, _count_eq_right)
+
+"""
+    _count_greater(i::Int, x::V)
+    _count_lesser(i::Int, x::V)
+    _count_g_left(i::Int, x::V)
+    _count_l_left(i::Int, x::V)
+    _count_g_right(i::Int, x::V)
+    _count_l_right(i::Int, x::V)
+Count the number of elements greater/lesser than `x[i]` (optionally to the left/right of `x[i]`). Extended method to vector with sig `(x::V)` are generated.
+"""
+function _count_greater(i::Int, x::V) where {T <: Number,V <: AbstractVector{T}}
+    return count(y -> x[i] < y, x)
+end
+function _count_lesser(i::Int, x::V) where {T <: Number,V <: AbstractVector{T}}
+    return count(y -> x[i] > y, x)
+end
+function _count_g_left(i::Int, x::V) where {T <: Number,V <: AbstractVector{T}}
+    return _count_greater(i, @view x[1:i])
+end
+function _count_l_left(i::Int, x::V) where {T <: Number,V <: AbstractVector{T}}
+    return _count_lesser(i, @view x[1:i])
+end
+function _count_g_right(i::Int, x::V) where {T <: Number,V <: AbstractVector{T}}
+    return _count_greater(1, @view x[i:end])
+end
+function _count_l_right(i::Int, x::V) where {T <: Number,V <: AbstractVector{T}}
+    return _count_lesser(1, @view x[i:end])
+end
+# Generating vetorized versions
+lazy(_count_greater, _count_g_left, _count_g_right)
+lazy(_count_lesser, _count_l_left, _count_l_right)
+
+"""
+    _count_eq_param(i::Int, x::V, param::T)
+    _count_l_param(i::Int, x::V, param::T)
+    _count_g_param(i::Int, x::V, param::T)
+Count the number of elements equal to (resp. lesser/greater than) `x[i] + param`. Extended method to vector with sig `(x::V, param::T)` are generated.
+"""
+function _count_eq_param(i::Int, x::V, param::T) where {T <: Number,V <: AbstractVector{T}}
+    return count(y -> y == x[i] + param, x)
+end
+function _count_l_param(i::Int, x::V, param::T) where {T <: Number,V <: AbstractVector{T}}
+    return count(y -> y < x[i] + param, x)
+end
+function _count_g_param(i::Int, x::V, param::T) where {T <: Number,V <: AbstractVector{T}}
+    return count(y -> y > x[i] + param, x)
+end
+# Generating vetorized versions
+lazy_param(_count_eq_param, _count_l_param, _count_g_param)
+
+"""
+    _count_bounding_param(i::Int, x::V, param::T)
+Count the number of elements bounded (not strictly) by `x[i]` and `x[i] + param`. An extended method to vector with sig `(x::V, param::T)` is generated.
+"""
+function _count_bounding_param(i::Int, x::V, param::T
+) where {T <: Number,V <: AbstractVector{T}}
+    return count(y -> x[i] ≤ y ≤ x[i] + param, x)
+end
+# Generating vetorized versions
+lazy_param(_count_bounding_param)
+
+"""
+    _val_minus_param(i::Int, x::V, param::T)
+    _param_minus_val(i::Int, x::V, param::T)
+Return the difference `x[i] - param` (resp. `param - x[i]`) if positive, `0.0` otherwise.  Extended method to vector with sig `(x::V, param::T)` are generated.
+"""
+function _val_minus_param(i::Int, x::V, param::T
+) where {T <: Number,V <: AbstractVector{T}}
+    return max(0, x[i] - param)
+end
+function _param_minus_val(i::Int, x::V, param::T
+) where {T <: Number,V <: AbstractVector{T}}
+    return max(0, param - x[i])
+end
+# Generating vetorized versions
+lazy_param(_val_minus_param, _param_minus_val)
+
+"""
+    _contiguous_vals_minus(i::Int, x::V)
+    _contiguous_vals_minus_rev(i::Int, x::V)
+Return the difference `x[i] - x[i + 1]` (resp. `x[i + 1] - x[i]`) if positive, `0.0` otherwise. Extended method to vector with sig `(x::V)` are generated.
+"""
+function _contiguous_vals_minus(i::Int, x::V) where {T <: Number,V <: AbstractVector{T}}
+    return length(x) == i ? 0 : _val_minus_param(i, x, x[i + 1])
+end
+function _contiguous_vals_minus_rev(i::Int, x::V
+) where {T <: Number,V <: AbstractVector{T}}
+    return length(x) == i ? 0 : _param_minus_val(i, x, x[i + 1])
+end
+# Generating vetorized versions
+lazy(_contiguous_vals_minus, _contiguous_vals_minus_rev)
diff --git a/src/utils.jl b/src/utils.jl
new file mode 100644
index 0000000..0afbcac
--- /dev/null
+++ b/src/utils.jl
@@ -0,0 +1,20 @@
+
+"""
+    _map_tr(f, x)
+    _map_tr(f, x, param)
+Return an anonymous function that applies `f` to all elements of `x`, with an optional parameter `param`.
+"""
+_map_tr(f, x) = ((g, y) -> map(i -> g(i, y), 1:length(y)))(f, x)
+_map_tr(f, x, param) = ((g, y, p) -> map(i -> g(i, y, p), 1:length(y)))(f, x, param)
+
+"""
+    lazy(funcs::Function...)
+    lazy_param(funcs::Function...)
+Generate methods extended to a vector instead of one of its components. For `lazy` (resp. `lazy_param`) a function `f` should have the following signature: `f(i::Int, x::V)` (resp. `f(i::Int, x::V, param::T)`).
+"""
+function lazy(funcs::Function...)
+    foreach(f -> eval(:($f(x) = (y -> _map_tr($f, y))(x))), map(Symbol, funcs))
+end
+function lazy_param(funcs::Function...)
+    foreach(f -> eval(:($f(x, param) = (y -> _map_tr($f, y, param))(x))), map(Symbol, funcs))
+end
diff --git a/test/layers.jl b/test/layers.jl
new file mode 100644
index 0000000..72bd50a
--- /dev/null
+++ b/test/layers.jl
@@ -0,0 +1,154 @@
+# Transformation layer
+data = [
+    [1, 5, 2, 4, 3] => 2,
+    [1, 2, 3, 2, 1] => 2,
+]
+
+# Test transformations without parameters
+funcs = Dict(
+    ICN._identity => [
+        data[1].first,
+        data[2].first,
+    ],
+    ICN._count_eq => [
+        [0, 0, 0, 0, 0],
+        [1, 1, 0, 1, 1],
+    ],
+    ICN._count_eq_right => [
+        [0, 0, 0, 0, 0],
+        [1, 1, 0, 0, 0],
+    ],
+    ICN._count_eq_left => [
+        [0, 0, 0, 0, 0],
+        [0, 0, 0, 1, 1],
+    ],
+    ICN._count_greater => [
+        [4, 0, 3, 1, 2],
+        [3, 1, 0, 1, 3],
+    ],
+    ICN._count_lesser => [
+        [0, 4, 1, 3, 2],
+        [0, 2, 4, 2, 0],
+    ],
+    ICN._count_g_left => [
+        [0, 0, 1, 1, 2],
+        [0, 0, 0, 1, 3],
+    ],
+    ICN._count_l_left => [
+        [0, 1, 1, 2, 2],
+        [0, 1, 2, 1, 0],
+    ],
+    ICN._count_g_right => [
+        [4, 0, 2, 0, 0],
+        [3, 1, 0, 0, 0],
+    ],
+    ICN._count_l_right => [
+        [0, 3, 0, 1, 0],
+        [0, 1, 2, 1, 0],
+    ],
+    ICN._contiguous_vals_minus => [
+        [0, 3, 0, 1, 0],
+        [0, 0, 1, 1, 0],
+    ],
+    ICN._contiguous_vals_minus_rev => [
+        [4, 0, 2, 0, 0],
+        [1, 1, 0, 0, 0],
+    ],
+)
+
+for (f, results) in funcs, (key, vals) in enumerate(data)
+    @test f(vals.first) == results[key]
+end
+
+# Test transformations with parameter
+funcs_param = Dict(
+    ICN._count_eq_param => [
+        [1, 0, 1, 0, 1],
+        [1, 0, 0, 0, 1],
+    ],
+    ICN._count_l_param => [
+        [2, 5, 3, 5, 4],
+        [4, 5, 5, 5, 4],
+    ],
+    ICN._count_g_param => [
+        [2, 0, 1, 0, 0],
+        [0, 0, 0, 0, 0],
+    ],
+    ICN._count_bounding_param => [
+        [3, 1, 3, 2, 3],
+        [5, 3, 1, 3, 5],
+    ],
+    ICN._val_minus_param => [
+        [0, 3, 0, 2, 1],
+        [0, 0, 1, 0, 0],
+    ],
+    ICN._param_minus_val => [
+        [1, 0, 0, 0, 0],
+        [1, 0, 0, 0, 1],
+    ],
+)
+
+for (f, results) in funcs_param, (key, vals) in enumerate(data)
+    @test f(vals.first, vals.second) == results[key]
+end
+
+# arithmetic layer
+@test ICN._sum(map(p -> p.first, data)) == [2, 7, 5, 6, 4]
+@test ICN._prod(map(p -> p.first, data)) == [1, 10, 6, 8, 3]
+
+# aggregation layer
+@test ICN._sum(data[1].first) == 15
+@test ICN._sum(data[2].first) == 9
+
+@test ICN._count_positive(data[1].first) == 5
+@test ICN._count_positive(data[2].first) == 5
+@test ICN._count_positive([1, 0, 1, 0, 1]) == 3
+
+# Comparison layer
+data = [3 => (1, 5), 5 => (10, 5)]
+
+funcs = [
+    ICN._identity => [3, 5],
+]
+
+# test no param/vars
+for (f, results) in funcs, (key, vals) in enumerate(data)
+    @test f(vals.first) == results[key]
+end
+
+funcs_param = [
+    ICN._abs_diff_val_param => [2, 5],
+    ICN._val_minus_param => [2, 0],
+    ICN._param_minus_val => [0, 5],
+]
+
+for (f, results) in funcs_param, (key, vals) in enumerate(data)
+    @test f(vals.first, vals.second[1]) == results[key]
+end
+
+funcs_vars = [
+    ICN._abs_diff_val_vars => [2, 0],
+    ICN._val_minus_vars => [0, 0],
+    ICN._vars_minus_val => [2, 0],
+]
+
+for (f, results) in funcs_vars, (key, vals) in enumerate(data)
+    @test f(vals.first, rand(1:10, vals.second[2])) == results[key]
+end
+
+
+funcs_param_dom = [
+    ICN._euclidian_param => [3.5, 2.0],
+]
+
+for (f, results) in funcs_param_dom, (key, vals) in enumerate(data)
+    @test f(vals.first, vals.second[1], vals.second[2]) ≈ results[key]
+end
+
+funcs_dom = [
+    ICN._euclidian => [8/3, 2.0],
+]
+
+for (f, results) in funcs_dom, (key, vals) in enumerate(data)
+    @test f(vals.first, vals.second[2]) ≈ results[key]
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 1d3b8a0..324e9cf 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,6 +1,8 @@
 using CompositionalNetworks
 using Test
 
+ICN = CompositionalNetworks
+
 @testset "CompositionalNetworks.jl" begin
-    # Write your tests here.
+    include("layers.jl")
 end