man: more bibliographic references

* spot/bin/man/autfilt.x, spot/bin/man/dstar2tgba.x,
spot/bin/man/ltlfilt.x: Add more bibliography.

spot/bin/man/autfilt.x

@@ -23,7 +23,22 @@ Proceedings of SPIN'15.  LNCS 9232.
 
 That paper gives the motivation for options \fB\-\-exclusive\-ap\fR
 and \fB\-\-simplify\-exclusive\-ap\fR.
+.TP
+\(bu
+Thibaud Michaud and Alexandre Duret-Lutz:
+Practical stutter-invariance checks for ω-regular languages.
+Proceedings of SPIN'15.  LNCS 9232.
+
+Describes the algorithms used by the \fB\-\-destut\fR and
+\fB\-\-instut\fR options.  These options correpond respectively to
+cl() and sl() in the paper.
+.TP
+\(bu
+Souheib Baarir and Alexandre Duret-Lutz: SAT-based minimization of
+deterministic ω-automata.  Proceedings of LPAR'15 (a.k.a LPAR-20).
+LNCS 9450.
 
+Describes the \fB\-\-sat\-minimize\fR option.
 [SEE ALSO]
 .BR spot-x (7)
 .BR dstar2tgba (1)

spot/bin/man/dstar2tgba.x

@@ -94,6 +94,14 @@ LNCS 8461.
 Explains the SAT-based minimization techniques that can be used (on
 request only) by dstar2tgba to minimize deterministic Büchi automata.
 
+.TP
+5.
+Souheib Baarir and Alexandre Duret-Lutz: SAT-based minimization of
+deterministic ω-automata.  Proceedings of LPAR'15 (a.k.a LPAR-20).
+LNCS 9450.
+
+Extends the previous paper by allowing arbitrary acceptance
+conditions.
 [SEE ALSO]
 .BR spot-x (7),
 .BR autfilt (1)

spot/bin/man/ltlfilt.x

@@ -20,6 +20,13 @@ stutter-invariant LTL. Information Processing Letters 75(6): 261-263
 Describes the transformation behind the \fB\-\-remove\-x\fR option.
 .TP
 \(bu
+Thibaud Michaud and Alexandre Duret-Lutz:
+Practical stutter-invariance checks for ω-regular languages.
+Proceedings of SPIN'15.  LNCS 9232.
+
+Describes the algorithm used by \fB\-\-stutter\-insensitive\fR option.
+.TP
+\(bu
 Christian Dax, Jochen Eisinger, Felix Klaedtke: Mechanizing the
 Powerset Construction for Restricted Classes of
 ω-Automata. Proceedings of ATVA'07.  LNCS 4762.