Fixed reducing functions description

parser/README.md

@@ -32,7 +32,7 @@ Functions:
 | `asin` | $\sin^{-1}(x)$ |
 | `asinh` | $\sinh^{-1}(x)$ |
 | `atan` | $\tan^{-1}(x)$ |
-| `avg` | $\overline x$ |
+| `avg` | $\overline X$ |
 | `cos` | $\cos(x)$ |
 | `cosh` | $\cosh(x)$ |
 | `cot` | $\cot(x)$ |
@@ -58,6 +58,6 @@ Floating points: `.`, `,`
 
 Functions have only one argument, provided in braces. Operators must have two operands except minus (if it is the first character of equation or braced expression).
 
-`sum` and `prod` sums and multiplies all elements in variable if it is `numpy.ndarray` and produces a `float`.
+`avg`, `sum` and `prod` applied on `numpy.ndarray` produce `float`.
 
 **! There is no error handling yet !**