Define for types (finitely satisfiable maximal sets of formulas with parameters in some model $\mathcal M$) $p,q$ :
$p \vDash q$
when every sequence realizing p realizes q.
Why it suffices to test that for every FINITE $q' \subseteq q$ there is a finite $p' \subseteq p$ such that $p' \vDash q'$ ?
