View source for Template:MT book:examples:1:1:1

{{MT_Ex |
example = It might seems -at first sight- that a semialgebra it's a very restricted subset of <math>
\mathcal{P}(X)</math>, but it's easy to prove that with <math> X = \mathbb{R} </math> the class : 

::<math>\qquad \mathcal{S} = \{(a,b] :  a \leq b \in \mathbb{R} \} </math>  

it's a semialgebra over <math> \mathbb{R}</math> and clearly this set is non-trivial.
}}