Help with CFrame?

I was playing around with CFrames , and I tried calling this method called "CFrame:inverse()" on line 30 but the output says:

Players.Player1.PlayerGui.Script:30: attempt to call method 'inverse' (a nil value)

How would I call this method correctly?

Updated script

Player = game.Players.LocalPlayer
Character = Player.Character
Torso = Character.Torso
Mouse = Player:GetMouse()
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function CharacterCheck()
    if not Character or Character.Parent == nil then
    Character = Player.CharacterAdded:wait()
    end
end
CharacterCheck()
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function MakeWelds()
    local Arms = {Character["Left Arm"],
                  Character["Right Arm"]
    }
    local ArmWelds = {}
    for i,v in pairs (Arms) do
        local Weld = Instance.new("Weld",Torso)
        Weld.Name = v.Name.." Weld"
        Weld.Part0 = Torso
        Weld.Part1 = v
        ArmWelds[i] = Weld
    end
    return ArmWelds
end
Welds = MakeWelds()
Welds[1].C0 = CFrame.new(1.5,0,0)
Welds[2].C0 = CFrame.new(-1.5,0,0)
Welds[1].C0 = Welds[1].C0:inverse()
Welds[1].C0 = CFrame.Angles(Weld.C0.CFrame*CFrame.Angles(0,1,0))
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