Select the most appropriate one-word substitution for the given group of words. 

Walk before hand or an introductory statement of a book or rule etc

Preamble

The most appropriate one-word substitution for the given group of words is preamble.

• Preamble is an introductory statement that explains the purpose of a document or law.
• Epilogue is a concluding statement that comes at the end of a book or play.
• Precursor is something that comes before and leads to something else.
• Index is a list of topics or terms in a book or document, with the page numbers where they can be found.