Purchase is related to Payment. Payment is related to Involved. 
Sack is related to Bed. Bed is related to Secret. Secret is related to Word. Word is related to Writing. 
Purchase <--RelatedTo--> Payment <--RelatedTo--> Involved 
Sack <--RelatedTo--> Bed <--RelatedTo--> Secret <--RelatedTo--> Word <--RelatedTo--> Writing 