let F be Graph-yielding Function; :: thesis: ex p being one-to-one Function st
( dom p = dom F & rng p = dom F & ( for x being object st x in dom F holds
ex G1, G2 being _Graph st
( G1 = F . x & G2 = F . (p . x) & G2 is G1 -isomorphic ) ) )

reconsider p = id (dom F) as one-to-one Function ;
take p ; :: thesis: ( dom p = dom F & rng p = dom F & ( for x being object st x in dom F holds
ex G1, G2 being _Graph st
( G1 = F . x & G2 = F . (p . x) & G2 is G1 -isomorphic ) ) )

thus ( dom p = dom F & rng p = dom F ) ; :: thesis: for x being object st x in dom F holds
ex G1, G2 being _Graph st
( G1 = F . x & G2 = F . (p . x) & G2 is G1 -isomorphic )

let x be object ; :: thesis: ( x in dom F implies ex G1, G2 being _Graph st
( G1 = F . x & G2 = F . (p . x) & G2 is G1 -isomorphic ) )

assume A6: x in dom F ; :: thesis: ex G1, G2 being _Graph st
( G1 = F . x & G2 = F . (p . x) & G2 is G1 -isomorphic )

then reconsider G = F . x as _Graph by GLIB_000:def 53;
take G ; :: thesis: ex G2 being _Graph st
( G = F . x & G2 = F . (p . x) & G2 is G -isomorphic )

take G ; :: thesis: ( G = F . x & G = F . (p . x) & G is G -isomorphic )
thus G = F . x ; :: thesis: ( G = F . (p . x) & G is G -isomorphic )
thus G = F . (p . x) by A6, FUNCT_1:18; :: thesis: G is G -isomorphic
thus G is G -isomorphic by GLIB_010:53; :: thesis: verum