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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def define_unit( symbol, value, tex_repr=None, offset=None, prefixable=False, registry=None ):
 """ Define a new unit and add it to the specified unit registry. Parameters symbol : string The symbol for the new unit. value : tuple or :class:`unyt.array.unyt_quantity` The definition of the new unit in terms of some other units. For example, one would define a new "mph" unit with ``(1.0, "mile/hr")`` or with ``1.0*unyt.mile/unyt.hr`` tex_repr : string, optional The LaTeX representation of the new unit. If one is not supplied, it will be generated automatically based on the symbol string. offset : float, optional The default offset for the unit. If not set, an offset of 0 is assumed. prefixable : boolean, optional Whether or not the new unit can use SI prefixes. Default: False registry : :class:`unyt.unit_registry.UnitRegistry` or None The unit registry to add the unit to. If None, then defaults to the global default unit registry. If registry is set to None then the unit object will be added as an attribute to the top-level :mod:`unyt` namespace to ease working with the newly defined unit. See the example below. Examples -------- 42.0 dimensionless """

    from unyt.array import unyt_quantity, _iterable
    import unyt

    if registry is None:
        registry = default_unit_registry
    if symbol in registry:
        raise RuntimeError(
            "Unit symbol '%s' already exists in the provided " "registry" % symbol
        )
    if not isinstance(value, unyt_quantity):
        if _iterable(value) and len(value) == 2:
            value = unyt_quantity(value[0], value[1], registry=registry)
        else:
            raise RuntimeError(
                '"value" needs to be a quantity or ' "(value, unit) tuple!"
            )
    base_value = float(value.in_base(unit_system="mks"))
    dimensions = value.units.dimensions
    registry.add(
        symbol,
        base_value,
        dimensions,
        prefixable=prefixable,
        tex_repr=tex_repr,
        offset=offset,
    )
    if registry is default_unit_registry:
        u = Unit(symbol, registry=registry)
        setattr(unyt, symbol, u)