# 'ReversePropagation.jl' package

**URL:** <https://discourse.julialang.org/t/reversepropagation-jl-package/103779>\
**Category:** General Usage\
**Tags:** question, package\
**Created:** [September 12, 2023, 10:11am UTC](https://discourse.julialang.org/t/reversepropagation-jl-package/103779 "2023-09-12T10:11:31Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Ashu](https://avatars.discourse-cdn.com/v4/letter/a/4bbf92/32.png) [@Ashu](https://discourse.julialang.org/u/Ashu)\
**Post date:** [September 12, 2023, 10:11am UTC](https://discourse.julialang.org/t/reversepropagation-jl-package/103779/1 "2023-09-12T10:11:31Z")

</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

```

Thank you