split definitions and declarations, move to "tc" namespace

solver.h

@@ -0,0 +1,37 @@
+#pragma once
+
+#include "groups.h"
+#include <vector>
+
+namespace tc {
+    struct Cosets {
+        int ngens;
+        std::vector<int> data;
+        int len;
+
+        Cosets(int ngens, const std::vector<int> &data);
+
+        void add_row();
+
+        void put(int coset, int gen, int target);
+
+        void put(int idx, int target);
+
+        [[nodiscard]] int get(int coset, int gen) const;
+
+        [[nodiscard]] int get(int idx) const;
+    };
+
+    struct RelTable {
+        int gens[2]{};
+        int mult;
+        std::vector<int *> lst_ptr;
+        std::vector<int> gen;
+
+        explicit RelTable(Mult m);
+
+        int add_row();
+    };
+
+    Cosets solve(const Group &g, const std::vector<int> &sub_gens = {});
+}