In Erlang, when do I use ; or , or .?

I like to read semicolon as OR, comma as AND, full stop as END. So

foo(X) when X > 0; X < 7 ->
    Y = X * 2,
    case Y of
        12 -> bar;
        _  -> ook
    end;
foo(0) -> zero.

reads as

foo(X) when X > 0 *OR* X < 7 ->
    Y = X * 2 *AND*
    case Y of
        12 -> bar *OR*
        _  -> ok
    end *OR*
foo(0) -> zero *END*

This should make it clear why there is no ; after the last clause of a case.