THE FIRST formal operational schema we described had to be the schema of combination operations, since the lattice structure which characterizes the system of propositional operations implies a combinatorial system. On the other hand the second operational schema, which we are now going to study, derives from the group structure and the reversibility by inversion which is its distinctive feature. As we will elaborate at greater length in the following discussion, the system of formal operations constitutes both a lattice and a group and thus unites transformations by reciprocity and transformations by inversion into a single cluster.