class Net::LDAP::Filter

def negate(filter)

x = ~Net::LDAP::Filter.present("objectclass")
# attribute.
# Selects only entries that do not have an objectclass

as ~filter.
Negates a filter. Calling Fitler.negate(filter) i s the same
# 
def negate(filter)
  new(:not, filter, nil)
end