substitution for the variables in A and free variables in V. Then ΑΘ is in
T
D
(I) (resp., Γ
0
(/')) if and only if V6 is true wit / (resp., /'). By part
(a),
we may assume that each c
{
is in L. By Theorem
3,
V is domain in-
dependent, so V0 is true wit / if and only if V0 is true wit /'. The result
follows immediately. •
THEOREM
7
Every allowed stratified database is domain independent.
Proof:
Let D be an allowed stratified database and L<L' languages that ex-
ten ...
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