# Stuck at simplifying boolean expression

I'm getting stuck at the following boolean expression.

$$z + (x'y) + (xy') + (xt') + (yt')$$

In my solutions it's simplified and the $(yt')$ term is gone. How do they simplify this? I really cant see it....

Many thanks!

• as i see it you're only allowing x and y to be different from the 2nd and 3rd terms, so only one of the 4th and 5th can be the case – danimal Jun 10 '15 at 17:11
• I think i understand what you mean but is there a simple theorem or rule to simplify it? – Stekke Jun 10 '15 at 17:18