Codes are sometimes created with a particular structure.  For example, Gray codes are a sequential code where predecessor and successor code words differ in exactly one bit.  This property wraps between the first and the last code words.  Here is an example of a 4-bit gray code:

• “0000”
• “0001”
• “0010”
• “0011”
• “0010”
• “0110”
• “0111”
• “0101”
• “0100”
• “1100”
• “1101”
• “1111”
• “1110”
• “1010”
• “1011”
• “1001”
• “1000”