4.5 Implication elimination

This one is simpler than the previous, since it does not deal with suppositions but with facts:

$$\begin{fitch*} \par m & A \Rightarrow B \\ \par n & A \\ \par \hline \par & B & E$\Rightarrow$\ m,n \par \end{fitch*}$$

Simply, if we are told that when $A$ also happens $B$ (that's what it means $A\Rightarrow B$), and they also tell us that now happens $A$, then we can assure that $B$.

This rule is also named modus ponens.