* typo fixed from bug #3117 report

docs/ref.tex

@@ -3334,7 +3334,7 @@ A shr 1  { same as A div 2, but faster}
 Not 1    { equals -2 }
 Not 0    { equals -1 }
 Not -1   { equals 0  }
-B shl 2  { same as B * 2 for integers }
+B shl 2  { same as B * 4 for integers }
 1 or 2   { equals 3 }
 3 xor 1  { equals 2 }
 \end{verbatim}