fix 0a asterisk explanation

Author: mluukkai

src/content/0/en/part0a.md

@@ -37,7 +37,7 @@ The course contains fourteen parts, the first of which is numbered 0 for consist
 
 Proceeding from part *n* to part *n+1* is not sensible before enough know-how of the topics in part *n* has been achieved. In pedagogic terms, the course uses [Mastery Learning](https://en.wikipedia.org/wiki/Mastery_learning), and you are only intended to proceed to the next part after doing enough of the exercises of the previous part.
 
-In parts 1-4 you are expected to do **all** of the exercises that are marked with an asterisk(*). Exercises marked with an asterisk count towards your final grade, but skipping them does not prevent you from doing the compulsory exercises in the next parts. Parts 5-13 do not have asterisk marked exercises since there is no similar dependency on previous parts.
+In parts 1-4 you are expected to do at least **all** of the exercises that are **not** marked with an asterisk(*). Exercises marked with an asterisk count towards your final grade, but skipping them does not prevent you from doing the compulsory exercises in the next parts. Parts 5-13 do not have asterisk marked exercises since there is no similar dependency on previous parts.
 
 The speed of completing the course is flexible.