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sav08:partial_congruences [2008/04/23 07:45] vkuncak |
sav08:partial_congruences [2008/04/26 17:42] damien |
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**Proof:** | **Proof:** | ||
- | Show that C^i(s) \cap T^2 = s$ for each $i \ge 0$. | + | Show $C^i(s) \cap T^2 = s$ for all $i \ge 0$, by induction. |
+ | |||
+ | * $i = 0$: s = s | ||
+ | |||
+ | * $i \rightarrow i+1$: | ||
+ | $C^{i+1}(s) \cap T^2 = C(C^i(s) \cap T^2) \cap T^2 $, by induction hypothesis $C^i(s) \cap T^2 =s$. | ||
+ | Thus $C(C^i(s) \cap T^2) \cap T^2 = C(s) \cap T^2$. | ||
+ | As $C$ adds only needed term for congruence, the added term are either not in $T^2$ or $s$ in not a congruence. | ||
+ | By hypothesis $s$ is a congruence, so $C(s) \cap T^2 = s$. | ||
+ | Therefore $C^{i+1}(s) \cap T^2 = s$. | ||
**Proof End.** | **Proof End.** | ||
+ | |||
+ | When checking a formula we compute congruences on a finite set of terms that occur in the formula. | ||
+ | |||
+ | We apply the congruence condition only to terms that already exist in the set, using congruence condition: | ||
+ | \[ | ||
+ | \begin{array}{l} | ||
+ | \forall x_1,\ldots,x_n,y_1,\ldots,y_n. \bigwedge_{i=1}^n (x_i,y_i) \in r\ \land \ f(x_1,\ldots,x_n) \in T \land f(y_1,\ldots,y_n) \in T \rightarrow \\ | ||
+ | (f(x_1,\ldots,x_n),f(y_1,\ldots,y_n)) \in r | ||
+ | \] | ||
+ |