[rand.eng.philox] Replace "the function f(x) returns" with "f(x) is".

Author: tkoeppe

source/numerics.tex

@@ -3152,12 +3152,14 @@
 where:
   \begin{itemize}
   \item
-  the $\mullo(\tcode{a}, \tcode{b}, \tcode{w})$ function returns
-  the low half of the modular multiplication of \tcode{a} and \tcode{b}: $(\tcode{a} \cdot \tcode{b}) \mod 2^w$,
+  $\mullo(\tcode{a}, \tcode{b}, \tcode{w})$ is
+  the low half of the modular multiplication of \tcode{a} and \tcode{b}:
+  $(\tcode{a} \cdot \tcode{b}) \mod 2^w$,
 
   \item
-  the $\mulhi(\tcode{a}, \tcode{b}, \tcode{w})$ function returns
-  the high half of the multiplication of \tcode{a} and \tcode{b}: $(\left\lfloor (\tcode{a} \cdot \tcode{b}) / 2^w \right\rfloor)$,
+  $\mulhi(\tcode{a}, \tcode{b}, \tcode{w})$ is
+  the high half of the modular multiplication of \tcode{a} and \tcode{b}:
+  $(\left\lfloor (\tcode{a} \cdot \tcode{b}) / 2^w \right\rfloor)$,
 
   \item
   $k = 0, \dotsc, n/2 - 1$ is the index in the sequences,