Check if x is a RealIntervalField_class.
EXAMPLES:
sage: from sage.rings.real_interval_field import is_RealIntervalField as is_RIF
sage: is_RIF(RIF)
True
Check if x is a RealIntervalFieldElement.
EXAMPLES:
sage: from sage.rings.real_interval_field import is_RealIntervalFieldElement as is_RIFE
sage: is_RIFE(RIF(2.5))
True