function single(variable in list WHERE predicate)

Returns true if the predicate holds for exactly one of the elements in the list.

Arguments:
list: An expression that returns a list.
variable: This is the variable that can be used from the predicate.
predicate: A predicate that is tested against all items in the list.

Example Query:
    MATCH p=(n)-->(b)
    WHERE n.name='Alice' AND SINGLE (var IN nodes(p) WHERE var.eyes = "blue")
    RETURN p