Check if the given string consists of only letters and spaces and if every letter is in lower case.

Examples

letters_only("PYTHON") ➞ false

letters_only("python") ➞ true

letters_only("12321313") ➞ false

letters_only("i have spaces") ➞ true

letters_only("i have numbers(1-10)") ➞ false

letters_only("") ➞ false

Notes

• Empty arguments will always return false.
• Input values will be mixed (symbols, letters, numbers).