problem with normal subgroups of a finitely generated group

[Santymax98]

Hello, I am working with the following group

$$K = \langle \tau, \eta \mid \tau^n = 1, \eta^m = \tau^g, \eta \tau \eta^{-1} = \tau^h \rangle,$$

where the parameters $(m, n, g, h) \in \mathbb{N}^4$ satisfy the following restrictions:

1. $g < n$
2. $h < n$
3. $n \mid g(h - 1)$
4. $n \mid (h^m - 1)$

I have the following function to create the finitely presented group

function metacyclic_group(m::Int, n::Int, g::Int, h::Int)
    # Validate the restrictions
    if g >= n
        error("g must be greater than  n")
    end
    if h >= n
        error("h must be less than n")
    end
    if mod(g * (h - 1), n) != 0
        error("n must divide g(h - 1)")
    end
    if mod(h^m - 1, n) != 0
        error("n must divide h^m - 1")
    end

    # Create a free group with two generators, τ and η
    F = free_group(:τ, :η)
    
    # Defining generators
    τ = F[1]
    η = F[2]
    
    # Define the relationships for the metacylic group
    relations = [τ^n, η^m * τ^(-g), η * τ * η^(-1) * τ^(-h)]
    
    # Create the finitely presented group using the relations
    metacyclic_group = quo(F, relations)
    
    return metacyclic_group[1]
end

I can use the following

# Example usage:
m = 2 # Order of η
n = 15 # Order of τ
g = 5 # Parameter g
h = 4 # Parameter h

# Create the metacyclic group with the given values
G = metacyclic_group(m, n, g, h)
S = subgroups(G)
X = collect(S)
typeof(G)

All of the above works correctly but when I want to get the normal subgroups I get the following error

N = normal_subgroups(G)
ERROR: MethodError: Cannot `convert` an object of type SubFPGroup to an object of type FPGroup

Closest candidates are:
  convert(::Type{T}, ::T) where T
   @ Base Base.jl:84
  (::Type{S})(::T) where {S<:Union{FinGenAbGroup, Oscar.GAPGroup}, T<:Oscar.GAPGroup}
   @ Oscar ~/.julia/packages/Oscar/38HwK/src/Groups/homomorphisms.jl:900

Stacktrace:
 [1] setindex!(A::Vector{FPGroup}, x::SubFPGroup, i1::Int64)
   @ Base ./array.jl:1021
 [2] _as_subgroups(G::FPGroup, subs::GapObj)
   @ Oscar ~/.julia/packages/Oscar/38HwK/src/Groups/sub.jl:163
 [3] normal_subgroups(G::FPGroup)
   @ Oscar ~/.julia/packages/Oscar/38HwK/src/Groups/sub.jl:200
 [4] top-level scope
   @ ~/Metaciclicos/code_meta.jl:60

I would really appreciate if someone could help me with this problem.

[joschmitt]

Thank you for the report. This appears to be a bug to me, I opened #4276.

[joschmitt]

This is fixed in master now. It might take some time until we make a release and one gets this fix via an update. You can of course use the developer version of OSCAR until then (via ] dev Oscar in julia) if you like.

Thanks again, please let us know if you have further problems or encounter other errors.

[Santymax98]

Thanks for the information, I will keep an eye on the new update and in the meantime I will work with the developer version.