genltl: add a new family from SYNTCOMP'2017

* bin/genltl.cc, spot/gen/formulas.cc, spot/gen/formulas.hh: Implement
  it.
* tests/core/genltl.test: Test it.
* NEWS: Document it.

NEWS

@@ -2,6 +2,10 @@ New in spot 2.4.0.dev (not yet released)
 
   Tools:
 
+  - genltl learned to generate a new family of formulas, taken from
+    the SYNTCOMP competition on reactive synthesis:
+    --gf-equiv=RANGE      (GFa{1} & GFa{2} & ... & GFa{n}) <-> GFz
+
   - genltl learned to generate 4 new families of formulas, taken
     from Müller & Sickert's GandALF'17 paper:
     --ms-example=RANGE     GF(a1&X(a2&X(a3&...)))&F(b1&F(b2&F(b3&...)))

bin/genltl.cc

@@ -61,7 +61,7 @@ enum {
 static const argp_option options[] =
   {
     /**************************************************/
-    // Keep this alphabetically sorted (expect for aliases).
+    // Keep this alphabetically sorted (except for aliases).
     { nullptr, 0, nullptr, 0, "Pattern selection:", 1},
     // J. Geldenhuys and H. Hansen (Spin'06): Larger automata and less
     // work for LTL model checking.
@@ -86,6 +86,8 @@ static const argp_option options[] =
       "(range should be included in 1..12)", 0 },
     { "fxg-or", gen::LTL_FXG_OR, "RANGE", 0,
       "F(p0 | XG(p1 | XG(p2 | ... XG(pn))))", 0},
+    { "gf-equiv", gen::LTL_GF_EQUIV, "RANGE", 0,
+      "(GFa1 & GFa2 & ... & GFan) <-> GFz", 0},
     { "gh-q", gen::LTL_GH_Q, "RANGE", 0,
       "(F(p1)|G(p2))&(F(p2)|G(p3))&...&(F(pn)|G(p{n+1}))", 0 },
     { "gh-r", gen::LTL_GH_R, "RANGE", 0,

spot/gen/formulas.cc

@@ -41,6 +41,18 @@ namespace spot
   {
     namespace
     {
+      static formula
+      LTL_GF_equiv(int n, const std::string& a, const std::string& z)
+      {
+        std::vector<formula> gfs;
+        for (int i = 0; i < n; ++i)
+          gfs.emplace_back(formula::G(formula::F(
+                  formula::ap(a + std::to_string(i+1)))));
+
+        return formula::Equiv(formula::And(gfs),
+                              formula::G(formula::F(formula::ap(z))));
+      }
+
       static formula
       ms_example(const char* a, const char* b, int n)
       {
@@ -1159,6 +1171,8 @@ namespace spot
           return eh_pattern(n);
         case LTL_FXG_OR:
           return FXG_or_n("p", n);
+        case LTL_GF_EQUIV:
+          return LTL_GF_equiv(n, "a", "z");
         case LTL_GH_Q:
           return Q_n("p", n);
         case LTL_GH_R:
@@ -1239,6 +1253,7 @@ namespace spot
           "dac-patterns",
           "eh-patterns",
           "fxg-or",
+          "gf-equiv",
           "gh-q",
           "gh-r",
           "go-theta",
@@ -1296,6 +1311,7 @@ namespace spot
         case LTL_EH_PATTERNS:
           return 12;
         case LTL_FXG_OR:
+        case LTL_GF_EQUIV:
         case LTL_GH_Q:
         case LTL_GH_R:
         case LTL_GO_THETA:

spot/gen/formulas.hh

@@ -190,6 +190,7 @@ namespace spot
       LTL_DAC_PATTERNS,
       LTL_EH_PATTERNS,
       LTL_FXG_OR,
+      LTL_GF_EQUIV,
       LTL_GH_Q,
       LTL_GH_R,
       LTL_GO_THETA,

tests/core/genltl.test

@@ -157,3 +157,15 @@ ms-phi-h=3,170
 ms-phi-h=4,1816
 EOF
 diff out exp
+
+genltl --gf-equiv=0..5 --format=%F=%L,%f |
+  ltl2tgba -G -D -F-/2 --stats='%<,%s' > out
+cat >exp<<EOF
+gf-equiv=0,1
+gf-equiv=1,4
+gf-equiv=2,8
+gf-equiv=3,21
+gf-equiv=4,81
+gf-equiv=5,431
+EOF
+diff out exp