In 1965, Dmitri Borgmann noted that this expression:

11 + 2 – 1 = 12

… is valid also when interpreted as a set of characters:

11 “+ 2” = 112; 112 “- 1” = 12

… as a set of Roman numerals:

XI + II = XIII; XIII – I = XII

… and even as a set of letters:

ELEVEN + TWO = ELEVENTWO
ELEVENTWO – ONE = LEVETW (= TWELVE)