Hi Trevor - Thanks for the point you made about
the possible confusion with "i" and "l" - you may have a point as I've just typed a small "I" and "L"
and they do look somewhat similar. I was also
reminded of this when I worked on a recent xword
and the chemical symbol for thallium came up.
It seems that it's written "Tl" (capital T and small
L) which I've found rather puzzling.