Write a regular expression that checks if a string is a valid initial. Valid initials either look like (ex. for Chandler Muriel Bing):

• C. B.
• C. M. B.

Rules for a valid initial:

1. Each letter must be upper case.
2. Each letter must be immediately followed by a period.
3. There must be exactly one space separating each letter-period pair.
4. Leading or trailing whitespaces are valid.

Examples

"C. B." ➞ true

"    C. B." ➞ true
# Leading and trailing spaces are OK!

"C. B. k." ➞ false
# One of the initials is lower cased 

"C B" ➞ false
# Missing a dot to immediately follow. 

Notes

This challenge is designed to use RegEx only.