reserve x,x1,x2,y,y9,y1,y2,z,z1,z2 for object,P,X,X1,X2,Y,Y1,Y2,V,Z for set;

theorem Th16:
  for f being PartFunc of {x},Y holds rng f c= {f.x}
proof
  let f be PartFunc of {x},Y;
  dom f = {} or dom f = {x} by ZFMISC_1:33;
  hence thesis by FUNCT_1:4,RELAT_1:42;
end;
