((fn/complement :empty?) [])
((fn/complement :empty?) [a])
((fn/complement :fn/identity) false)
((fn/complement :fn/identity) 1)
((fn/complement :fn/identity) null)
((fn/complement :fn/identity) 0)
((fn/complement :fn/identity) [])
((fn/complement :fn/identity) "")
((fn/complement (fn [] null)))
((fn/complement :=) 1 1)
((fn/complement :=) 1 1 1 2)