function iff (x,y,z)
if a[x][y][z]==1 then
turtle.select(1)
elseif a[x][y][z]==2 then
turtle.select(2)
elseif a[x][y][z]==3 then
turtle.select(3)
elseif a[x][y][z]==4 then
turtle.select(4)
elseif a[x][y][z]==5 then
turtle.select(5)
elseif a[x][y][z]==6 then
turtle.select(6)
elseif a[x][y][z]==0 then
turtle.select(16)
end
end