# Return the lower case version of self.
	# If self is not a letter, then return self
	#
	#     assert 'A'.to_lower  == 'a'
	#     assert 'a'.to_lower  == 'a'
	#     assert '$'.to_lower  == '$'
	fun to_lower: Char
	do
		if is_upper then
			return (code_point + ('a'.distance('A'))).code_point
		else
			return self
		end
	end