reserve p,p1,p2,q,r,F,G,G1,G2,H,H1,H2 for ZF-formula,
  x,x1,x2,y,y1,y2,z,z1,z2,s,t for Variable,
  a,X for set;

theorem
  the_argument_of F 'or' G = 'not' F '&' 'not' G & the_antecedent_of F
  'or' G = 'not' F & the_consequent_of F 'or' G = G
proof
  thus the_argument_of F 'or' G = 'not' F '&' 'not' G by Th3;
  F 'or' G = 'not' F => G;
  hence thesis by Th6;
end;
