Attempt to index global "event" (nil value)

I am new to lua and have tried looking at other posts with a similar error. I could not solve my problem.

I try to remove my number objects using alpha on the orientation and the correct ones appear. I added the onOrientationLeft function and the listener for it. After that, I got my error and cannot figure out how to make it work. The comments in my code will illustrate what I'm trying to do, find the onOrientationLeft function and the latest runtime that references it.

pZeroButton = display.newImage ("0.png",100, 470 )
llZeroButton = display.newImage ("0.png", 200,200)
llZeroButton.alpha = 0

pOneButton = display.newImage ("1.png",56,420)

pTwoButton = display.newImage ("2.png",123.5, 420)

pThreeButton = display.newImage ("3.png",191,420)

pFourButton = display.newImage ("4.png",56,370)

pFiveButton = display.newImage ("5.png",123.5, 370)

pSixButton = display.newImage ("6.png",191,370)

pSevenButton = display.newImage ("7.png",56,320 )

pEightButton = display.newImage ("8.png",123.5,320)

pNineButton = display.newImage ("9.png", 191, 320)



function onOrientationLeft ()
if (event.type == "landscapeRight") then
    print ("Test if this function onOrientationLeft is working properly") 
end
end 

- [[I added this function, trying to force the function to print a string, but every time I rotate the phone in the crown SDK syntax, I get an error attempt to index global - "event" (nil value -]]

function calculateZero(number)
local pZeroButton = display.newText (0, 300,30,nil,38)
pZeroButton: setFillColor (0,0,0)
return
end



function calculateOne(number)
local pOneButton = display.newText (1, 300,30,nil,38)
pOneButton: setFillColor (0,0,0)
return
end

function calculateTwo(number)
local pTwoButton = display.newText (2, 300,30,nil,38)
pTwoButton: setFillColor (0,0,0)
return
end

function calculateThree(number)
local pThreeButton = display.newText (3, 300,30,nil,38)
pThreeButton: setFillColor (0,0,0)
return
end

function calculateFour(number)
local pFourButton = display.newText (4, 300,30,nil,38)
pFourButton: setFillColor (0,0,0)
return
end

function calculateFive(number)
local pFiveButton = display.newText (5, 300,30,nil,38)
pFiveButton: setFillColor (0,0,0)
return
end

function calculateSix(number)
local pSixButton = display.newText (6, 300,30,nil,38)
pSixButton: setFillColor (0,0,0)
return
end

function calculateSeven(number)
local pSevenButton = display.newText (7, 300,30,nil,38)
pSevenButton: setFillColor (0,0,0)
return
end

function calculateEight(number)
local pEightButton = display.newText (8, 300,30,nil,38)
pEightButton: setFillColor (0,0,0)
return
end

function calculateNine(number)
local pNineButton = display.newText (9, 300,30,nil,38)
pNineButton: setFillColor (0,0,0) 
return
end



pZeroButton : addEventListener ("tap", calculateZero)

pOneButton : addEventListener ("tap", calculateOne)

pTwoButton : addEventListener ("tap", calculateTwo)

pThreeButton : addEventListener ("tap", calculateThree)

pFourButton : addEventListener ("tap", calculateFour)

pFiveButton : addEventListener ("tap", calculateFive)

pSixButton : addEventListener ("tap", calculateSix)

pSevenButton : addEventListener ("tap", calculateSeven)

pEightButton : addEventListener ("tap", calculateEight)

pNineButton : addEventListener ("tap", calculateNine)


Runtime : addEventListener ("orientation", onOrientationLeft)