apart

test if a list of elements are not all contained in one part of the partition

letting P be partition({1,2},{3},{4,5,6})
find a: bool such that a = apart({3,5},P) $true

The result of these syntaxes is true, because elements 3 and 5 ({3,5}) are not all contained in one part of the partition ({1,2},{3},{4,5,6})

See it demonstrated here.