theorem Th48:
  Vars(p => q,V) = Vars(p,V) \/ Vars(q,V)
proof
A1: the_consequent_of p => q = q by QC_LANG2:30;
  p => q is conditional & the_antecedent_of p => q = p by QC_LANG2:30,def 11;
  hence thesis by A1,Th47;
end;
