reserve x,y,y1,y2 for set;
reserve C for non empty set;
reserve c for Element of C;
reserve f,h,g,h1 for Membership_Func of C;

theorem
  f c= 1_minus g implies g c= 1_minus f
proof
  1_minus 1_minus f = f;
  hence thesis by Th35;
end;
