let p be FinSequence of NAT ; :: thesis: for T, T1 being DecoratedTree st p in dom T holds
for q being FinSequence of NAT st q in dom (T with-replacement (p,T1)) & q in { t1 where t1 is Element of dom T : not p is_a_prefix_of t1 } holds
(T with-replacement (p,T1)) . q = T . q

let T, T1 be DecoratedTree; :: thesis: ( p in dom T implies for q being FinSequence of NAT st q in dom (T with-replacement (p,T1)) & q in { t1 where t1 is Element of dom T : not p is_a_prefix_of t1 } holds
(T with-replacement (p,T1)) . q = T . q )

assume A1: p in dom T ; :: thesis: for q being FinSequence of NAT st q in dom (T with-replacement (p,T1)) & q in { t1 where t1 is Element of dom T : not p is_a_prefix_of t1 } holds
(T with-replacement (p,T1)) . q = T . q

let q be FinSequence of NAT ; :: thesis: ( q in dom (T with-replacement (p,T1)) & q in { t1 where t1 is Element of dom T : not p is_a_prefix_of t1 } implies (T with-replacement (p,T1)) . q = T . q )
assume that
A2: q in dom (T with-replacement (p,T1)) and
A3: q in { t1 where t1 is Element of dom T : not p is_a_prefix_of t1 } ; :: thesis: (T with-replacement (p,T1)) . q = T . q
per cases ( ( not p is_a_prefix_of q & (T with-replacement (p,T1)) . q = T . q ) or ex r being FinSequence of NAT st
( r in dom T1 & q = p ^ r & (T with-replacement (p,T1)) . q = T1 . r ) )
by A1, A2, Th11;
suppose ( not p is_a_prefix_of q & (T with-replacement (p,T1)) . q = T . q ) ; :: thesis: (T with-replacement (p,T1)) . q = T . q
hence (T with-replacement (p,T1)) . q = T . q ; :: thesis: verum
end;
suppose A4: ex r being FinSequence of NAT st
( r in dom T1 & q = p ^ r & (T with-replacement (p,T1)) . q = T1 . r ) ; :: thesis: (T with-replacement (p,T1)) . q = T . q
ex t9 being Element of dom T st
( q = t9 & not p is_a_prefix_of t9 ) by A3;
hence (T with-replacement (p,T1)) . q = T . q by ; :: thesis: verum
end;
end;