Worked, thanks

Type checking worked thanks alot, now How do I plot an equation like x=2 or x=Pi/2??

I've played a bit with NumericEvent and I have managed not to get an error when I run the proc however I sitll have the wrong operation to check wheter the derivative exists or not and to plot and X=t where t is the x coord where the derivative would not exist (Pi/2 for tan)