A palindrome is a word, number, phrase, or other sequence of characters which reads the same backward as forward, such as ‘’taco cat’’ or madam or racecar or the number 10801. Sentence-length palindromes may be written when allowances are made for adjustments to capital letters, punctuation, and word dividers, such as "A man, a plan, a canal, Panama!", "Was it a car or a cat I saw?" or "No 'x' in Nixon". Composing literature in palindromes is an example of constrained writing. The word palindrome was first published by Henry Peacham in his book, The Truth of Our Times (1638). It is derived from the Greek roots palin (πάλιν; "again") and dromos (δρóμος; "way, direction"); however, the Greek language uses a different word, i.e. καρκινικός, to refer to letter-by-letter reversible writing.