procedure ackertrace(i,j)
static level
local result
initial level := 0
write(repl("x",level +:= 1))
if i = 0 then result := j + 1
else if j = 0 then result := ackertrace(i - 1,1)
else result := ackertrace(i - 1,ackertrace(i,j - 1))
level -:= 1
return result
end