Gexercise 19.7 suppose you are given a rebltion r \vith four attributes ab()d. f'or each of the following sets of fds, assurning those are the only dependencies that hold for r, do the following: (a) identify the candidate key(s) for r. (b) identify the best honnal forbl thatr satisfies (lnf, 2nf, : jnf, or benf). (c) if ii is not in bcnl~\ decolnpose it into a set of bcnf relations that preserve the dependencies. 1. c: - d, + a. 13 c 2. fj '-~-f c'. d --> a : 3. abc -~f d, d --> a 4. a -+ b. b(} ,. d. a ~. c 5. a13 c, ab···_··.• d. c -+ a, d·_·-+ 13

Write a new lc-3 trap subroutine (i.e. a subroutine that will be invoked via the trap instruction) that will receive a numeric digit entered at the keyboard (i.e. an ascii character), echo it to the screen, and return in r0 the corresponding numeric value: so if the user types the digit '7', the character '7' will appear on the screen, but the value returned in r0 will be b0000 0000 0000 0111 (#7) you may not use any trap calls in your code - you must implement the "polling" code that interrogates the keyboard status and data registers. ; getnum_tsr ; a subroutine for obtaining a numeric value ; given ascii numeric digit input to keyboard. ; the numeric digit is echoed to the console (e.g. '7' = b0000 0000 0011 0111), ; but the value returned in r0 is the actual numeric value ; corresponding to the digit (e.g. b0000 0000 0000 0111 =