The system of equations to solve is

x - 2y = i
x + 2y = j

which leads to

x = (j+i)/2
y = (j-i)/4

OK, good point ;-)
Added this to description:

draw([1,0,1,0,1,0,1,0])

■□■□■□■□

And added this to testcase:

var wave5=
"■□■□■□■□";

Test.assertSimilar(draw([1,0,1,0,1,0,1,0]), wave5)

Thanks for your feedback ;-)

Corrected the name. Hopefully it should work. If it works could you mark the issue as resolved?
Thanks for your post!

Yes I saw that "fst" is badly sorted:-) Anyway, thanks for your post!

I think you should print the two given arrays so that we see what happens. There should be no errors - though random is random -:) because @Unnamed who is excellent passed the F# kata without problem. I just tried a few solutions and they worked fine.

Do you pass the fixed tests? Do you know which test you are failing?

Oh, a F#-guy! :-) What about creating new F#-katas for the community? :-)

Thanks for your feedback!