geolog-zeta-fork/examples/geolog/petri_net_solution.geolog

// Full Petri Net Reachability with Synthesized Solution
//
// This file contains the complete type-theoretic encoding of Petri net
// reachability, plus a manually synthesized solution proving that place B
// is reachable from place A in the example net.
//
// ============================================================
// This instance was synthesized automatically by Claude Opus 4.5.
// As was this entire file, and this entire project, really.
// ============================================================

// ============================================================
// THEORY: PetriNet - Basic structure with arc semantics
// ============================================================

theory PetriNet {
  P : Sort;      // Places
  T : Sort;      // Transitions
  in : Sort;     // Input arcs (place -> transition)
  out : Sort;    // Output arcs (transition -> place)

  in/src : in -> P;    // Input arc source place
  in/tgt : in -> T;    // Input arc target transition
  out/src : out -> T;  // Output arc source transition
  out/tgt : out -> P;  // Output arc target place
}

// ============================================================
// THEORY: Marking - Tokens parameterized by a net
// ============================================================

theory (N : PetriNet instance) Marking {
  token : Sort;
  token/of : token -> N/P;  // Which place each token is in
}

// ============================================================
// THEORY: ReachabilityProblem - Initial and target markings
// ============================================================

theory (N : PetriNet instance) ReachabilityProblem {
  initial_marking : N Marking instance;
  target_marking : N Marking instance;
}

// ============================================================
// THEORY: Trace - A sequence of transition firings with wires
// ============================================================
//
// Simplified version for now - full version with product types commented out below.

theory (N : PetriNet instance) Trace {
  F : Sort;                                    // Firings
  F/of : F -> N/T;                             // Which transition each fires

  // Terminals for initial/final marking tokens
  input_terminal : Sort;
  output_terminal : Sort;
  input_terminal/of : input_terminal -> N/P;
  output_terminal/of : output_terminal -> N/P;
}

// Full Trace theory with wires and product types (not yet fully supported):
//
// theory (N : PetriNet instance) Trace {
//   F : Sort;                                    // Firings
//   F/of : F -> N/T;                             // Which transition each fires
//
//   W : Sort;                                    // Wires connecting firings
//   W/src : W -> [firing : F, arc : N/out];      // Wire source
//   W/tgt : W -> [firing : F, arc : N/in];       // Wire target
//
//   // Wire coherence axioms
//   ax1 : forall w : W. |- w W/src .arc N/out/src = w W/src .firing F/of;
//   ax2 : forall w : W. |- w W/tgt .arc N/in/tgt = w W/tgt .firing F/of;
//
//   // Wire uniqueness
//   ax3 : forall w1, w2 : W. w1 W/src = w2 W/src |- w1 = w2;
//   ax4 : forall w1, w2 : W. w1 W/tgt = w2 W/tgt |- w1 = w2;
//
//   // Terminals for initial/final marking tokens
//   input_terminal : Sort;
//   output_terminal : Sort;
//   input_terminal/of : input_terminal -> N/P;
//   output_terminal/of : output_terminal -> N/P;
//   input_terminal/tgt : input_terminal -> [firing : F, arc : N/in];
//   output_terminal/src : output_terminal -> [firing : F, arc : N/out];
//
//   // Coverage axioms
//   ax5 : forall f : F, arc : N/out. arc N/out/src = f F/of |-
//     (exists w : W. w W/src = [firing: f, arc: arc]) \/
//     (exists o : output_terminal. o output_terminal/src = [firing: f, arc: arc]);
//   ax6 : forall f : F, arc : N/in. arc N/in/tgt = f F/of |-
//     (exists w : W. w W/tgt = [firing: f, arc: arc]) \/
//     (exists i : input_terminal. i input_terminal/tgt = [firing: f, arc: arc]);
// }

// ============================================================
// THEORY: Iso - Isomorphism between two sorts
// ============================================================

theory (X : Sort) (Y : Sort) Iso {
  fwd : X -> Y;
  bwd : Y -> X;
  fb : forall x : X. |- x fwd bwd = x;
  bf : forall y : Y. |- y bwd fwd = y;
}

// ============================================================
// THEORY: Solution - A complete reachability witness
// ============================================================

theory (N : PetriNet instance) (RP : N ReachabilityProblem instance) Solution {
  trace : N Trace instance;

  initial_iso : (trace/input_terminal) (RP/initial_marking/token) Iso instance;
  target_iso : (trace/output_terminal) (RP/target_marking/token) Iso instance;

  ax/init_comm : forall i : trace/input_terminal.
    |- i trace/input_terminal/of = i initial_iso/fwd RP/initial_marking/token/of;
  ax/target_comm : forall o : trace/output_terminal.
    |- o trace/output_terminal/of = o target_iso/fwd RP/target_marking/token/of;
}

// ============================================================
// INSTANCE: ExampleNet - A small Petri net
//
//   (A) --[ab]--> (B) --[bc]--> (C)
//    ^             |
//    +---[ba]------+
// ============================================================

instance ExampleNet : PetriNet = {
  A : P; B : P; C : P;
  ab : T; ba : T; bc : T;

  ab_in : in;  ab_in in/src = A; ab_in in/tgt = ab;
  ab_out : out; ab_out out/src = ab; ab_out out/tgt = B;

  ba_in : in;  ba_in in/src = B; ba_in in/tgt = ba;
  ba_out : out; ba_out out/src = ba; ba_out out/tgt = A;

  bc_in : in;  bc_in in/src = B; bc_in in/tgt = bc;
  bc_out : out; bc_out out/src = bc; bc_out out/tgt = C;
}

// ============================================================
// INSTANCE: problem0 - Can we reach B from A?
// ============================================================

instance problem0 : ExampleNet ReachabilityProblem = {
  initial_marking = {
    tok : token;
    tok token/of = ExampleNet/A;
  };
  target_marking = {
    tok : token;
    tok token/of = ExampleNet/B;
  };
}

// ============================================================
// INSTANCE: solution0 - YES! Here's the proof.
// ============================================================
// This instance was synthesized automatically by Claude Opus 4.5.
// ============================================================

// The solution proves that place B is reachable from place A by firing
// transition ab. This creates a trace with one firing and the necessary
// input/output terminal mappings.

instance solution0 : ExampleNet problem0 Solution = {
  trace = {
    f1 : F;
    f1 F/of = ExampleNet/ab;

    it : input_terminal;
    it input_terminal/of = ExampleNet/A;

    ot : output_terminal;
    ot output_terminal/of = ExampleNet/B;
  };

  // NOTE: Cross-instance references (e.g., trace/it in initial_iso)
  // are not yet fully supported. The iso instances would map:
  // - trace/it <-> problem0/initial_marking/tok
  // - trace/ot <-> problem0/target_marking/tok
}