let E be non empty set ; :: thesis: for f being Function of E,E
for c being Element of Class (=_ f)
for e being Element of c holds f . e in c
let f be Function of E,E; :: thesis: for c being Element of Class (=_ f)
for e being Element of c holds f . e in c
let c be Element of Class (=_ f); :: thesis: for e being Element of c holds f . e in c
let e be Element of c; :: thesis: f . e in c
dom f = E by FUNCT_2:def 1;
then A1: f . e in (dom f) \/ (rng f) by XBOOLE_0:def 3;
ex x9 being object st
( x9 in E & c = Class ((=_ f),x9) ) by EQREL_1:def 3;
then A2: c = Class ((=_ f),e) by EQREL_1:23;
(iter (f,1)) . e = f . e by FUNCT_7:70
.= (id (field f)) . (f . e) by A1, FUNCT_1:17
.= (iter (f,0)) . (f . e) by FUNCT_7:68 ;
then [(f . e),e] in =_ f by Def7;
hence f . e in c by A2, EQREL_1:19; :: thesis: verum