Consider the two expressions $\backslash$sigma $\backslash$theta $($E$1$ E$2)$ and $\backslash$sigma $\backslash$theta $($E$1$ E$2).$

a$.$ Show using an example that the two expressions are not equivalent in general.

b$.$ Give a simple condition on the predicate $\backslash$theta $,$ which if satisfied will ensure that the two expressions

are equivalent.