1. For a term u, let u be the expression obtained from u by replacing the variable x by the term t. Restate this definition without using any form of the word replace or its synonyms. Suggestion: Use recursion on u. (Observe that from the new definition it is clear that u is itself a term.) 1. For a term u, let u be the expression obtained from u by replacing the variable x by the term t. Restate this definition without using any form of the word replace or its synonyms. Suggestion: Use recursion on u. (Observe that from the new definition it is clear that u is itself a term.)