# Bounds are not contracting using 'ReversePropagation.jl'

**URL:** https://discourse.julialang.org/t/bounds-are-not-contracting-using-reversepropagation-jl/103846
**Category:** General Usage
**Tags:** question, package
**Created:** [September 14, 2023, 11:29am UTC](https://discourse.julialang.org/t/bounds-are-not-contracting-using-reversepropagation-jl/103846 "2023-09-14T11:29:40Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![Ashu](https://avatars.discourse-cdn.com/v4/letter/a/4bbf92/32.png) [@Ashu](https://discourse.julialang.org/u/Ashu)
#### Post date: [September 14, 2023, 11:29am UTC](https://discourse.julialang.org/t/bounds-are-not-contracting-using-reversepropagation-jl/103846/1 "2023-09-14T11:29:40Z")

</div>

Hello,

I am trying to run an example code given for illustrating the working of `ReversePropagation.jl`. But it is neither working in `Pluto.jl` notebook nor in `VSCode`. Could anyone please check if I am making any mistakes? The code is:

```julia
using Symbolics
using IntervalArithmetic
using ReversePropagation

vars = @variables x, y
	    
ex = x^2 + y^2
    
C = forward_backward_contractor(ex, vars) # construct the contractor

constraint = Interval(0, 1)

X = IntervalBox(Interval(-10,10), 2)

C(X, constraint)

```

Error-1:

```julia
C = forward_backward_contractor(ex, vars) # construct the contractor
ERROR: MethodError: rev(::typeof(+), ::Num, ::Num, ::Num) is ambiguous.

```

Error-2:

```julia
C(X, constraint)
ERROR: UndefVarError: `C` not defined

```