The class of weakly algebrizable logics is defined as the class of logics having monotonic and injective Leibniz operator. We show that \monotonicity" can- not be discarded on this definition, by presenting an example of a system with injective and non monotonic Leibniz operator. We also show that the non injectivity of the non protoalgebraic inf-sup fragment of the Classic Propositional Calculus, CPC_{inf,sup}, holds only from the fact that the empty set is a CPC_{inf,sup}-filter.

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