Fix math containing %!!!

Doc/ref.tex

@@ -503,10 +503,10 @@ Division by zero raises a {\tt RuntimeError} exception.
 The \verb|'%'| operator yields the remainder from the division
 of the first argument by the second.
 The numeric arguments are first converted to a common type.
-The outcome of $x % y$ is defined as $x - y*trunc(x/y)$.
+The outcome of $x \% y$ is defined as $x - y*trunc(x/y)$.
 A zero right argument raises a {\tt RuntimeError} exception.
 The arguments may be floating point numbers, e.g.,
-$3.14 % 0.7$ equals $0.34$.
+$3.14 \% 0.7$ equals $0.34$.
 
 \section{Arithmetic expressions}
 

Doc/ref/ref.tex

@@ -503,10 +503,10 @@ Division by zero raises a {\tt RuntimeError} exception.
 The \verb|'%'| operator yields the remainder from the division
 of the first argument by the second.
 The numeric arguments are first converted to a common type.
-The outcome of $x % y$ is defined as $x - y*trunc(x/y)$.
+The outcome of $x \% y$ is defined as $x - y*trunc(x/y)$.
 A zero right argument raises a {\tt RuntimeError} exception.
 The arguments may be floating point numbers, e.g.,
-$3.14 % 0.7$ equals $0.34$.
+$3.14 \% 0.7$ equals $0.34$.
 
 \section{Arithmetic expressions}