Hey,

I am having trouble proving...

$\displaystyle \sigma \rightarrow Y \vdash (\phi \lor \sigma ) \to (\phi \lor Y) $

I know that the beginning hypotheses are $\displaystyle \sigma \rightarrow Y $ and $\displaystyle (\phi \lor \sigma )$, but I am not sure how to break down the "or" statement.

Thanks!