support for TFF0 with arith
enable $to_int, $to_rat, $to_real, $is_int
work on $ite_t/$ite_f
regression tests for FOF/CNF/TFF/TFA, and a fix for pretty-printing output status according to SZS ontology
model output for tptp also in pretty-printer
work on $let_**
a variety of improvements to TPTP TFF parsing; only outstanding issue is $let_??, for which I've written to geoff sutcliffe