Definition:Substitution Instance

Definition
A substitution instance of a sequent $S_1$ is a sequent $S_2$ which results from $S_1$ by replacing one or more of the statement variables in some statement forms in $S_1$ throughout the whole of $S_1$ by other statement forms, as follows:


 * Every occurrence of a particular substituted statement variable is replaced by the same statement form;
 * Different statement variables may be replaced by different statement forms;
 * The substitution can be made only on statement variables.