Based on the given scenario the friendship function that their relationship fulfill is called practical goals.
Practical goals is a friendship function where friends support each other by rendering help to one another.
Based on the given scenario we can tend to say that both Joe and Bob friendship fulfill practical goals relationship function.
They both support each other and they have each other back based on the fact that joe is often ready to help his friend Bob and Bob is also ready to render assistance or help to Joe when even Joe out of town.
Inconclusion the friendship function that their relationship fulfill is called practical goals.
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