logic help

[physicsuser]

need to prove this


\frac{\urcorner P \equiv false}{P \equiv true}


here is what I did
using Leibniz


\frac{X \equiv Y}{E[z:=X] \equiv E[z:=Y]}



X=\urcorner P



Y=false



E:\urcorner z



z=z



\frac{\urcorner P \equiv false}{\urcorner\urcorner P \equiv \urcorner false}


since \urcorner\urcorner P \equiv P
and \urcorner false \equiv true


\frac{\urcorner P \equiv false}{P \equiv true}


is this a proof?