'X' Stands for Unknown

From Author Wars - https://authorwars.com/books/x-stands-for-unknown-3353206.html

Overview:

Title: 'X' Stands for Unknown
Author: Isaac Asimov
Year: 1986
Type: Non-fiction

Editions/Publications:

Unknown. X Stands for Unknown (Unknown, Isaac Asimov, Grafton, ISBN-10: 0586058427, £2.95, 270 pages, Paperback, Non-fiction)