Return is a type of Income. Trace is a type of Return. Pencil entails/necessarily involves Trace. 
Saving is related to Interest. Interest is related to Investment. Investment is a type of Skin. Skin is related to Cover. 
Income <--IsA-- Return <--IsA-- Trace <--Entails-- Pencil 
Saving <--RelatedTo--> Interest <--RelatedTo--> Investment --IsA--> Skin <--RelatedTo--> Cover 