5. [20 points) Not regular. Let the alphabet be {0,...,9,-,=}. Define SUBTRACTION = {w/w is a string 1 - y = z with I, y, z decimal numbers such that the equation is correct}. Leading O's are allowed. E.g., 13-007 = 6 E SUBTRACTION, 17 SUBTRACTION. Prove that SUBTRACTION is not regular. 17