Develop a structured flowchart and pseudocode outlining the merging of customer records for Geraldine's Landscaping Service and Gerard's Landscaping Service as they combine their businesses. The records to be consolidated include a unique customer number, last name, address, and property size in square feet. The objective is to create a unified customer file without duplicate customer numbers. Refer to Chapters $7$ and $8$ of Joyce Farrell's Programming Logic & Design for guidance in developing the program logic.

Do not forget to:

Declare your files

Open your files

Update your files

Close your files

Then, write the Python code.