'Returns the largest representable number smaller than a.
>>> c = ExtendedContext.copy()
>>> c.Emin = -999
>>> c.Emax = 999
>>> ExtendedContext.next_minus(Decimal(\'1\'))
Decimal(\'0.999999999\')
>>> c.next_minus(Decimal(\'1E-1007\'))
Decimal(\'0E-1007\')
>>> ExtendedContext.next_minus(Decimal(\'-1.00000003\'))
Decimal(\'-1.00000004\')
>>> c.next_minus(Decimal(\'Infinity\'))
Decimal(\'9.99999999E+999\')
>>> c.next_minus(1)
Decimal(\'0.999999999\')'

def next_minus(self, a):

    a = _convert_other(a, raiseit=True)
    return a.next_minus(context=self)
