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 Th35:
  f c= g iff 1_minus g c= 1_minus f
proof
  1_minus 1_minus f = f & 1_minus 1_minus g = g;
  hence thesis by Lm2;
end;
