  We study the positive logic FO+ on finite words, and its fragments, pursuing
and refining the work initiated in [Kuperberg 2023]. First, we transpose
notorious logic equivalences into positive first-order logic: FO+ is equivalent
to LTL+ , and its two-variable fragment FO2+ with (resp. without) successor
available is equivalent to UTL+ with (resp. without) the "next" operator X
available. This shows that despite previous negative results, the class of
FO+-definable languages exhibits some form of robustness. We then exhibit an
example of an FO-definable monotone language on one predicate, that is not
FO+-definable, refining the example from [Kuperberg 2023] with 3 predicates.
Moreover, we show that such a counter-example cannot be FO2-definable.
