why predicate<> sealed?

i wanted get category predicate<imyinterface>, nonetheless appears predicate<> sealed. box i wanted simply relapse inverted (!) outcome designated function. i have ways accomplish goal. doubt competence ms designers have pondering last sign predicate<>?

without many guess i came adult with:
(a) simplified testing, only vs cost trade off
(b) "no good" deriving predicate<>

what think?

update: there n predicates boldly total list predicates during an initialization phase. any jointly proud (if abc added, notabc can't added). i celebrated settlement looks like:

bool happy(imyinterface i) {...}
bool nothappy(imyinterface i) { relapse !happy(i); }
bool hungry(imyinterface i) {...}
bool nothungry(imyinterface i) { relapse !hungry(i); }
bool busy(imyinterface i) {...}
bool notbusy(imyinterface i) { relapse !busy(i); }
bool smart(imyinterface i) {...}
bool notsmart(imyinterface i) {...} //not simply !smart

its i can't solve problem, the i awe since i couldn't solve certain way.