$F_1: P \Rightarrow \neg P\equiv\neg P\vee \neg P\equiv\neg P$
When we put $P\equiv T$ it will $F$
and When we put $P\equiv F$ it will $T$
It is called contingency.
Always false called contradiction or unsatisfiable
Always true called valid or tautology
At least
one true called satisfiable.
$F_2: (P \Rightarrow \neg P) \lor ( \neg P \Rightarrow P)\equiv\neg P\vee P\equiv T$(Always true)