diff --git a/README.md b/README.md
index 892246f..b575c40 100644
--- a/README.md
+++ b/README.md
@@ -4,8 +4,10 @@
 Neural-Network representations of mixed quantum states and to find the Steady-
 State of dissipative Quantum Systems with variational Montecarlo schemes.
 
+This code has been developed while working on [Variational neural network ansatz for steady states in open quantum systems](https://arxiv.org/abs/1902.10104)
+
 ## Installation
-To Install `NeuralQuantum.jl`, please run the following commands to install all
+To Install `NeuralQuantum.jl`, run the following commands to install all
 dependencies:
 ```
 using Pkg
@@ -13,15 +15,14 @@ pkg"add https://github.com/PhilipVinc/QuantumLattices.jl"
 pkg"add https://github.com/PhilipVinc/ValueHistoriesLogger.jl"
 pkg"add https://github.com/PhilipVinc/NeuralQuantum.jl"
 ```
-If you are wondering what all those packages are for, here's an explanation:
+Those packages are needed for the following reasons:
  - `QuantumLattices` is a custom package that allows defining new types of operators on a lattice. It's not needed natively but it is usefull to define hamiltonians on a lattice.
- - `Optimisers`, a custom version of the still unreleased `FluxML/Optimisers.jl`, with features that are not yet released in the original branch.
  - `ValueHistoriesLogger` custom logger for logging arbitrary values
 
 ## Example
 ```
 # Load dependencies
-using NeuralQuantum, QuantumLattices, Optimisers
+using NeuralQuantum, QuantumLattices
 using Printf, ValueHistoriesLogger, Logging, ValueHistories
 
 # Select the numerical precision
diff --git a/src/States/NAryState.jl b/src/States/NAryState.jl
index 0701d0c..5d75c27 100644
--- a/src/States/NAryState.jl
+++ b/src/States/NAryState.jl
@@ -109,6 +109,20 @@ IntegerToState(n_sites, loc_dim, val, T::Type{<:Number}) =
     end
     arr
 end
+
+# --- Indexing function for local spaces used in operators
+local_index(s::NAryState, i::T) where {T<:Integer} =
+    T(s.σ[i])+1
+
+function local_index(s::NAryState{T,Nb}, is::Vector{T2}) where {T,Nb,T2<:Integer}
+    idx = 0
+    for (i, j)=enumerate(reverse(is))
+        idx += T2(s.σ[i]) * Nb^(j-1)
+    end
+    return idx + 1
+end
+# -- end
+
 # -------------- Base.show extension for nice printing -------------- #
 Base.show(io::IO, ::MIME"text/plain", bs::NAryState) = print(io, "NAryState(",bs.n,") : ", String(bs.σ,false),
                                            " = ", bs.i_σ)