(8*s1(x,y)-S1(x-1,y-1)-S1(x,y-1)-S1(x+1,y-1)-S1(x-1,y)-S1(x+1,y)-S1(x-1,y+1)-S1(x,y+1)-S1(x+1,y+1))*10+127.5

p.263, line 4 of the boxed program example:

p.264, line 13 of the bottom example: the string should be 'abcde'.

p.284, change the first line (line 20 of the code) to:

if elt==0: dx+=1; continue # if elt is 0, don't even

p.296, 3rd line on page (line 13 of the top example): the string should be 'abcde'.

p.301, line 5 of the boxed example should be

>>> lst.append('d')

p.370, in the formula for Gy, the second line should be

- I(x-1,y+1) - 2I(x,y+1) - I(x+1,y+1)