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;
reserve M for non empty set,
  m,m9 for Element of M,
  v,v9 for Function of VAR,M;
reserve i,j for Element of NAT;

theorem
  H is negative implies the_argument_of (H/(x,y)) = (the_argument_of H)/
  (x, y )
proof
  assume
A1: H is negative;
  then H/(x,y) is negative by Th168;
  then
A2: H/(x,y) = 'not' the_argument_of (H/(x,y)) by ZF_LANG:def 30;
  H = 'not' the_argument_of H by A1,ZF_LANG:def 30;
  hence thesis by A2,Th156;
end;
