Definitely put something at the level for INTERCAL that the .5 variable should be interpreted in your way. Otherwise there is no way to know.
Regarding Whenever you need to explain how the read() should be interpreted and please make a comma, so the syntax is correct.
Also it would need to be stated how to interpret the order of execution, since Whenever does not guarantee the order. Otherwise the sequence could as well start with "D E" or "F". For what it is worth the complete sequence could even be "F A B". Though with defining the order it would take all the fun of Whenever.
(That's the main reason I really dislike this level. I doesn't give you a fair chance.)
Also, regardless of the start, the way it is now your code will end up in an endless loop with line 6 being executed forever. (Line 3 actually has chance to be completely removed from the todo list.) So none of the solutions is correct for end is never reached. This can be easily fixed the same way as it is done for line 3.
I guess you will have to come up with some other code to make this work.