I am trying to complie this program and I get many errors, on every line starting at the 5thline, it do not like the variable b0 and b1 . This program is taken from a book and should work. Why am i getting all those errors

start:
Low 0
Low 1
POT 2,255,b0 '5
Pot 2,255,b1
IF b0 = b1 then start
IF b0 > b1 then greater
IF b0 < b1 then lesser
greater:
b2 = b0 -b1
if b2 > 10 then cw
goto start
lesser:
b2 =b1-b0
if b2>10 then ccw
goto start
cw:
high 0
pause 100
goto start
ccw:
high 1
pause 100
goto start