• I think following cmd is incorrect as the 'fstmakecontextfst' needs a phone list that includes disambiguation symbols.

• But this filter rule will remove all disambiguation symbols(&0, &1) and subsequential-symbol("#$")

(echo " 0"; echo "a 1"; echo "b 2"; echo "#0 3"; echo "#1 4"; echo "#$ 5" ) > phones.txt
( echo 3; echo 4 ) > disambig.list
fstmakecontextfst --read-disambig-syms=disambig.list <(grep -v '#' phones.txt) 5 ilabels.int > C.fst

• And in "fstmakecontextfst.cc", it adds 'loop_fst' , a loop for each phone and disambiguation symbol.

https://github.com/kaldi-asr/kaldi/blob/master/src/fstbin/fstmakecontextfst.cc#L113
The code is :

// 'loop_fst' will be an acceptor FST with single (initial and final) state, with
// a loop for each phone and disambiguation symbol.
StdVectorFst loop_fst;
loop_fst.AddState(); // Add state zero.
loop_fst.SetStart(0);
loop_fst.SetFinal(0, TropicalWeight::One());
for (size_t i = 0; i < phone_syms.size(); i++) {
int32 sym = phone_syms[i];
loop_fst.AddArc(0, StdArc(sym, sym, TropicalWeight::One(), 0));
}

• Which means variable 'phone_syms' should includes phone and disambiguation symbols.
• So grep -v "#\\$" phones.txt should work, Or change the example to "echo "$ 5""