Whenever I run my program I get an error statement saying “assertion failed!”. What is Wrong? Thanks in advance! 
local function onScreenTouch(event)
if event.x < centerX then
if (event.phase == “began”) then
x = event.x
y = event.y
tx = x
ty = y
elseif (event.phase == “moved”) then
tx = event.x
ty = event.y
elseif (event.phase == “ended”) then
x, y = 0, 0
tx, ty = 0, 0
end
end
return true
end
Runtime:addEventListener(“touch”, OnScreenTouch)
