# Returns true is self is not a number.
	#
	# As `nan != nan`, `is_nan` should be used to test if a float is the special *not a number* value.
	#
	# ~~~
	# assert nan != nan # By IEEE 754
	# assert nan.is_nan
	# assert not 10.0.is_nan
	# ~~~
	fun is_nan: Bool `{ return isnan(self); `}