add Antoine's comments

session_1/session_1.Rmd

@@ -248,7 +248,7 @@ To call mathematical function you must with `function_name(<number>)`.
 For example, for the natural logarithm:
 
 ```{r calculatorstep8, include=TRUE}
-log(1)  # natural logarithm
+log(2)  # natural logarithm
 ```
 
 ```{r calculatorstep9, include=TRUE}
@@ -402,7 +402,7 @@ This is called autocompletion, don't hesitate to spam your `tabulation` key as y
 
 Variable names can contain **letters**, **numbers**, **underscores** and **periods**.
 
-They **cannot start with a number** nor contain spaces at all.
+They **cannot start with a number or an underscore** nor contain spaces at all.
 
 Different people use different conventions for long variable names, these include: