'Initialize the dimension system.
It is important that base units have a name or a symbol such that
one can sort them in a unique way to define the vector basis.'

def __init__(self, base, dims=(), name='', descr=''):

    self.name = name
    self.descr = descr
    self._base_dims = self.sort_dims(base)
    self._dims = tuple((set(base) | set(dims)))
    if (self.is_consistent is False):
        raise ValueError(("The    system    with    basis    '%s'    is    not    consistent" % str(self._base_dims)))
