-Θ′ has the advantage that <code>f (Θ′ f)</code> really *reduces to* <code>Θ′ f</code>. <code>f (Y′ f)</code> is only convertible with <code>Y′ f</code>; that is, there's a common formula they both reduce to. For most purposes, though, either will do.
+Θ′ has the advantage that <code>f (Θ′ f)</code> really *reduces to* <code>Θ′ f</code>.
+
+<code>f (Y′ f)</code> is only convertible with <code>Y′ f</code>; that is, there's a common formula they both reduce to. For most purposes, though, either will do.