Description: The intersection of a class of transitive sets is transitive. Exercise
5(b) of Enderton p. 73. trintALT is an alternate proof of trint .
trintALT is trintALTVD without virtual deductions and was
automatically derived from trintALTVD using the tools program
translate..without..overwriting.cmd and the Metamath program "MM-PA>
MINIMIZE__WITH *" command. (Contributed by Alan Sare, 17-Apr-2012)(Proof modification is discouraged.)(New usage is discouraged.)