Minimum-Length Pangrammatic Ladders
A pangrammatic word ladder is one which contains at least one of every letter of the alphabet. Since letters in a ladder can be changed only one at a time, a minimum-length ladder of n-letter words contains 26 - n + 1 words.
Gordon, Leonard J.
"Minimum-Length Pangrammatic Ladders,"
Word Ways: Vol. 23
, Article 16.
Available at: https://digitalcommons.butler.edu/wordways/vol23/iss2/16