'Adds `min` operator that specifies lower bound for specific index.
:Parameters:
- `spec`: a list of field, limit pairs specifying the inclusive
lower bound for all keys of a specific index in order.
.. versionadded:: 2.7'

def min(self, spec):

    if (not isinstance(spec, (list, tuple))):
        raise TypeError('spec    must    be    an    instance    of    list    or    tuple')
    self.__check_okay_to_chain()
    self.__min = SON(spec)
    return self
