Difficult is related to Like. Like is related to Dad. Dad is related to Informal. Informal is a different concept from Formal. 
you are likely to find Cat in/at/on Box. Box is related to Open. Open is the opposite of Tight. 
Difficult <--RelatedTo--> Like <--RelatedTo--> Dad <--RelatedTo--> Informal <--DistinctFrom--> Formal 
Cat --AtLocation--> Box <--RelatedTo--> Open <--Antonym--> Tight 