diff --git a/src/test/nseq_zipt.cpp b/src/test/nseq_zipt.cpp
new file mode 100644
index 000000000..755c05c93
--- /dev/null
+++ b/src/test/nseq_zipt.cpp
@@ -0,0 +1,555 @@
+/*++
+Copyright (c) 2026 Microsoft Corporation
+
+Module Name:
+
+    nseq_zipt.cpp
+
+Abstract:
+
+    Unit tests for theory_nseq ported from the ZIPT test suite.
+    Source: https://github.com/CEisenhofer/ZIPT/blob/parikh/Test/Test.cs
+
+    Naming convention for strings/regexes (matching ZIPT's ParseStr/ParseRegex):
+      - Uppercase ASCII letters (A-Z) denote string variables.
+      - Lowercase letters and digits denote concrete characters.
+      - Regex syntax: * (Kleene star), + (one-or-more), | (union),
+        & (intersection), ~ (complement), ( ) (grouping).
+
+--*/
+#include "util/util.h"
+#include "ast/reg_decl_plugins.h"
+#include "ast/euf/euf_egraph.h"
+#include "ast/euf/euf_sgraph.h"
+#include "smt/seq/seq_nielsen.h"
+#include "ast/seq_decl_plugin.h"
+#include "ast/ast_pp.h"
+#include <iostream>
+#include <cassert>
+#include <functional>
+
+// -----------------------------------------------------------------------
+// Helper: build a string snode from a notation string.
+// Uppercase = fresh variable, lowercase/digit = concrete character.
+// Variables with the same letter share the same snode (memoised per call).
+// -----------------------------------------------------------------------
+struct str_builder {
+    euf::sgraph& sg;
+    euf::snode* vars[26] = {};      // vars['A'-'A'] .. vars['Z'-'A']
+
+    explicit str_builder(euf::sgraph& sg) : sg(sg) {}
+
+    euf::snode* var(char c) {
+        int idx = c - 'A';
+        if (!vars[idx])
+            vars[idx] = sg.mk_var(symbol(std::string(1, c).c_str()));
+        return vars[idx];
+    }
+
+    euf::snode* parse(const char* s) {
+        euf::snode* result = nullptr;
+        for (const char* p = s; *p; ++p) {
+            euf::snode* tok = (*p >= 'A' && *p <= 'Z')
+                ? var(*p)
+                : sg.mk_char((unsigned)(unsigned char)*p);
+            result = result ? sg.mk_concat(result, tok) : tok;
+        }
+        return result ? result : sg.mk_empty();
+    }
+};
+
+// -----------------------------------------------------------------------
+// Helper: build a regex snode from a notation string.
+// Parses: union (|), intersection (&), concatenation, postfix * and +,
+//         prefix complement ~, parentheses, lowercase chars, () for epsilon.
+// -----------------------------------------------------------------------
+struct regex_builder {
+    ast_manager& m;
+    seq_util& su;
+    euf::sgraph& sg;
+    sort* re_sort;
+
+    regex_builder(ast_manager& m, seq_util& su, euf::sgraph& sg)
+        : m(m), su(su), sg(sg) {
+        re_sort = su.re.mk_re(su.str.mk_string_sort());
+    }
+
+    euf::snode* parse(const char* s) {
+        int pos = 0;
+        expr_ref e = parse_union(s, pos, (int)strlen(s));
+        SASSERT(pos == (int)strlen(s));
+        return sg.mk(e.get());
+    }
+
+private:
+    expr_ref mk_char_re(char c) {
+        zstring zs(std::string(1, c).c_str());
+        return expr_ref(su.re.mk_to_re(su.str.mk_string(zs)), m);
+    }
+
+    expr_ref parse_union(const char* s, int& pos, int len) {
+        expr_ref left = parse_inter(s, pos, len);
+        while (pos < len && s[pos] == '|') {
+            ++pos;
+            expr_ref right = parse_inter(s, pos, len);
+            left = expr_ref(su.re.mk_union(left.get(), right.get()), m);
+        }
+        return left;
+    }
+
+    expr_ref parse_inter(const char* s, int& pos, int len) {
+        expr_ref left = parse_concat(s, pos, len);
+        while (pos < len && s[pos] == '&') {
+            ++pos;
+            expr_ref right = parse_concat(s, pos, len);
+            left = expr_ref(su.re.mk_inter(left.get(), right.get()), m);
+        }
+        return left;
+    }
+
+    expr_ref parse_concat(const char* s, int& pos, int len) {
+        expr_ref acc(m);
+        while (pos < len && s[pos] != ')' && s[pos] != '|' && s[pos] != '&') {
+            expr_ref tok = parse_repeat(s, pos, len);
+            acc = acc ? expr_ref(su.re.mk_concat(acc.get(), tok.get()), m) : tok;
+        }
+        return acc ? acc : expr_ref(su.re.mk_to_re(su.str.mk_string(zstring(""))), m);
+    }
+
+    expr_ref parse_repeat(const char* s, int& pos, int len) {
+        // collect leading tildes (complement)
+        int tildes = 0;
+        while (pos < len && s[pos] == '~') { ++tildes; ++pos; }
+        expr_ref base = parse_primary(s, pos, len);
+        // postfix * and +
+        while (pos < len && (s[pos] == '*' || s[pos] == '+')) {
+            if (s[pos] == '*')
+                base = expr_ref(su.re.mk_star(base.get()), m);
+            else
+                base = expr_ref(su.re.mk_plus(base.get()), m);
+            ++pos;
+        }
+        // apply complements
+        for (int i = 0; i < tildes; ++i)
+            base = expr_ref(su.re.mk_complement(base.get()), m);
+        return base;
+    }
+
+    expr_ref parse_primary(const char* s, int& pos, int len) {
+        if (pos >= len)
+            return expr_ref(su.re.mk_to_re(su.str.mk_string(zstring(""))), m);
+        char c = s[pos];
+        if (c == '(') {
+            ++pos;
+            expr_ref inner = parse_union(s, pos, len);
+            SASSERT(pos < len && s[pos] == ')');
+            ++pos;
+            return inner;
+        }
+        ++pos;
+        return mk_char_re(c);
+    }
+};
+
+// -----------------------------------------------------------------------
+// Test fixture: shared setup
+// -----------------------------------------------------------------------
+struct nseq_fixture {
+    ast_manager m;
+    euf::egraph eg;
+    euf::sgraph sg;
+    seq::nielsen_graph ng;
+    seq_util su;
+    str_builder sb;
+    regex_builder rb;
+
+    // Registers plugins on m and returns it so eg can be initialized after plugins are ready.
+    static ast_manager& init(ast_manager& m) { reg_decl_plugins(m); return m; }
+
+    nseq_fixture()
+        : eg(init(m)), sg(m, eg), ng(sg), su(m), sb(sg), rb(m, su, sg)
+    {}
+
+    euf::snode* S(const char* s) { return sb.parse(s); }
+    euf::snode* R(const char* s) { return rb.parse(s); }
+};
+
+static bool eq_sat(const char* lhs, const char* rhs) {
+    nseq_fixture f;
+    f.ng.add_str_eq(f.S(lhs), f.S(rhs));
+    return f.ng.solve() == seq::nielsen_graph::search_result::sat;
+}
+static bool eq_unsat(const char* lhs, const char* rhs) {
+    nseq_fixture f;
+    f.ng.add_str_eq(f.S(lhs), f.S(rhs));
+    return f.ng.solve() == seq::nielsen_graph::search_result::unsat;
+}
+static bool mem_sat(std::initializer_list<std::pair<const char*, const char*>> mems) {
+    nseq_fixture f;
+    for (auto& [str, re] : mems)
+        f.ng.add_str_mem(f.S(str), f.R(re));
+    return f.ng.solve() == seq::nielsen_graph::search_result::sat;
+}
+static bool mem_unsat(std::initializer_list<std::pair<const char*, const char*>> mems) {
+    nseq_fixture f;
+    for (auto& [str, re] : mems)
+        f.ng.add_str_mem(f.S(str), f.R(re));
+    return f.ng.solve() == seq::nielsen_graph::search_result::unsat;
+}
+
+// -----------------------------------------------------------------------
+// String equation tests  (ZIPT: CheckStrEquations)
+// -----------------------------------------------------------------------
+static void test_zipt_str_equations() {
+    std::cout << "test_zipt_str_equations\n";
+
+    VERIFY(eq_sat  ("abab", "XX"));       // abab = XX  (X="ab")
+    VERIFY(eq_sat  ("aX",   "YX"));       // aX = YX    (Y="a")
+    VERIFY(eq_sat  ("aX",   "Xa"));       // aX = Xa
+    VERIFY(eq_unsat("aX",   "Xb"));       // aX = Xb  — UNSAT
+    VERIFY(eq_sat  ("abX",  "Xba"));      // abX = Xba
+    VERIFY(eq_sat  ("XabY", "YbaX"));     // XabY = YbaX
+    VERIFY(eq_unsat("abcX", "Xbac"));     // abcX = Xbac — UNSAT
+    VERIFY(eq_unsat("aaX",  "Xa"));       // aaX = Xa   — UNSAT
+    VERIFY(eq_unsat("aa",   "XXX"));      // aa = XXX   — UNSAT
+    VERIFY(eq_sat  ("aX",   "XY"));       // aX = XY
+
+    std::cout << "  ok\n";
+}
+
+// -----------------------------------------------------------------------
+// Ground regex matching tests  (ZIPT: CheckRegexMatching)
+// No string variables — all concrete inputs.
+// -----------------------------------------------------------------------
+static void test_zipt_regex_ground() {
+    std::cout << "test_zipt_regex_ground\n";
+
+    VERIFY(mem_sat  ({{"", ""}}));                          // "" ∈ ε
+    VERIFY(mem_unsat({{"a", ""}}));                         // "a" ∉ ε
+
+    VERIFY(mem_sat  ({{"", "a*"}}));                        // "" ∈ a*
+    VERIFY(mem_sat  ({{"aaaa", "a*"}}));                    // "aaaa" ∈ a*
+    VERIFY(mem_unsat({{"b", "a*"}}));                       // "b" ∉ a*
+    VERIFY(mem_sat  ({{"abbb", "ab*"}}));                   // "abbb" ∈ ab*
+
+    VERIFY(mem_sat  ({{"ab", "(ab)+"}}));                   // "ab" ∈ (ab)+
+    VERIFY(mem_sat  ({{"ababab", "(ab)+"}}));               // "ababab" ∈ (ab)+
+    VERIFY(mem_unsat({{"", "(ab)+"}}));                     // "" ∉ (ab)+
+
+    VERIFY(mem_sat  ({{"", "()"}}));                        // "" ∈ ()
+    VERIFY(mem_sat  ({{"", "()*"}}));                       // "" ∈ ()*
+    VERIFY(mem_unsat({{"a", "()*"}}));                      // "a" ∉ ()*
+
+    VERIFY(mem_unsat({{"a", "~a"}}));                       // "a" ∉ ~a
+    VERIFY(mem_sat  ({{"b", "~a"}}));                       // "b" ∈ ~a
+    VERIFY(mem_sat  ({{"a", "~(~a)"}}));                    // "a" ∈ ~~a
+
+    VERIFY(mem_unsat({{"a", "a&(~a)"}}));                   // "a" ∉ a & ~a
+    VERIFY(mem_unsat({{"a", "(a|b)&(~a)"}}));               // "a" ∉ (a|b) & ~a
+    VERIFY(mem_sat  ({{"b", "(a|b)&(~a)"}}));               // "b" ∈ (a|b) & ~a
+
+    VERIFY(mem_sat  ({{"ab", "ab"}}));
+    VERIFY(mem_sat  ({{"a", "a|b"}}));
+    VERIFY(mem_sat  ({{"b", "a|b"}}));
+    VERIFY(mem_unsat({{"ab", "a|b"}}));
+
+    VERIFY(mem_sat  ({{"b", "(a|b)|(c|d)"}}));
+    VERIFY(mem_sat  ({{"c", "(a|b)|(c|d)"}}));
+    VERIFY(mem_unsat({{"e", "(a|b)|(c|d)"}}));
+    VERIFY(mem_sat  ({{"b", "(a|b)&(~a|b)"}}));
+    VERIFY(mem_unsat({{"a", "(a|b)&(~a|b)"}}));
+
+    VERIFY(mem_sat  ({{"abababab", "(ab)*"}}));
+    VERIFY(mem_sat  ({{"abab", "(ab)*"}}));
+    VERIFY(mem_unsat({{"aba", "(ab)*"}}));
+
+    VERIFY(mem_sat  ({{"c", "(a|b|c)&(c|d)"}}));
+    VERIFY(mem_unsat({{"b", "(a|b|c)&(c|d)"}}));
+
+    VERIFY(mem_sat  ({{"abab", "((ab)|(ba))+"}}));
+    VERIFY(mem_unsat({{"a", "((ab)|(ba))+"}}));
+
+    VERIFY(mem_sat  ({{"c", "(~a)&(c|b)"}}));
+
+    VERIFY(mem_unsat({{"a", "~(a|b)"}}));
+    VERIFY(mem_sat  ({{"c", "~(a|b)"}}));
+
+    std::cout << "  ok\n";
+}
+
+// -----------------------------------------------------------------------
+// String membership tests  (ZIPT: CheckStrMembership)
+// String variables (uppercase) combined with regex constraints.
+// -----------------------------------------------------------------------
+static void test_zipt_str_membership() {
+    std::cout << "test_zipt_str_membership\n";
+
+    // X ∈ (~(ab))*cab
+    VERIFY(mem_sat({{"X", "(~(ab))*cab"}}));
+
+    // X ∈ a* && X ∈ a* && X ∈ b+  → UNSAT
+    VERIFY(mem_unsat({{"X","a*"}, {"X","a*"}, {"X","b+"}}));
+
+    // X ∈ a*b* && Y ∈ a*b*  → SAT (independent)
+    VERIFY(mem_sat({{"X","a*b*"}, {"Y","a*b*"}}));
+
+    // X ∈ a* && Y ∈ (ab)+  → SAT (independent)
+    VERIFY(mem_sat({{"X","a*"}, {"Y","(ab)+"}}));
+
+    // X ∈ (ab)+ && X ∈ a*  → UNSAT
+    VERIFY(mem_unsat({{"X","(ab)+"}, {"X","a*"}}));
+
+    // XaX ∈ (aa)*  → UNSAT
+    VERIFY(mem_unsat({{"XaX", "(aa)*"}}));
+
+    // aX ∈ aa*
+    VERIFY(mem_sat({{"aX", "aa*"}}));
+
+    // X ∈ (aa)*a && X ∈ (aa)*  → UNSAT
+    VERIFY(mem_unsat({{"X","(aa)*a"}, {"X","(aa)*"}}));
+
+    // X ∈ (aa)*aa && X ∈ (aa)*  → SAT
+    VERIFY(mem_sat({{"X","(aa)*aa"}, {"X","(aa)*"}}));
+
+    // Xa ∈ aa*
+    VERIFY(mem_sat({{"Xa", "aa*"}}));
+
+    // Xa ∈ aa*a
+    VERIFY(mem_sat({{"Xa", "aa*a"}}));
+
+    // bX ∉ a*a
+    VERIFY(mem_unsat({{"bX", "a*a"}}));
+
+    // bX ∉ a*
+    VERIFY(mem_unsat({{"bX", "a*"}}));
+
+    // bX ∉ a*a
+    VERIFY(mem_unsat({{"bX", "a*a"}}));
+
+    // bX ∈ b*a
+    VERIFY(mem_sat({{"bX", "b*a"}}));
+
+    // bXb ∈ b*ab*
+    VERIFY(mem_sat({{"bXb", "b*ab*"}}));
+
+    // bXbb ∈ b*ab*
+    VERIFY(mem_sat({{"bXbb", "b*ab*"}}));
+
+    // XX ∈ aa*
+    VERIFY(mem_sat({{"XX", "aa*"}}));
+
+    // XaX ∈ aaa*
+    VERIFY(mem_sat({{"XaX", "aaa*"}}));
+
+    // XX ∈ aaaa*
+    VERIFY(mem_sat({{"XX", "aaaa*"}}));
+
+    // XbX ∉ a*
+    VERIFY(mem_unsat({{"XbX", "a*"}}));
+
+    // XbX ∈ a*b*
+    VERIFY(mem_sat({{"XbX", "a*b*"}}));
+
+    // XbX ∈ a*b*a*a
+    VERIFY(mem_sat({{"XbX", "a*b*a*a"}}));
+
+    // XabX ∉ (aba)*
+    VERIFY(mem_unsat({{"XabX", "(aba)*"}}));
+
+    // XaX ∉ (ab)*
+    VERIFY(mem_unsat({{"XaX", "(ab)*"}}));
+
+    // X ∈ a|b
+    VERIFY(mem_sat({{"X", "a|b"}}));
+
+    // XX ∉ a|b
+    VERIFY(mem_unsat({{"XX", "a|b"}}));
+
+    // XX ∉ (ab)|(ba)
+    VERIFY(mem_unsat({{"XX", "(ab)|(ba)"}}));
+
+    // XX ∈ (ab|ba)(ba|ab)
+    VERIFY(mem_sat({{"XX", "(ab|ba)(ba|ab)"}}));
+
+    // XX ∉ (ab|ba)(aa|bb)
+    VERIFY(mem_unsat({{"XX", "(ab|ba)(aa|bb)"}}));
+
+    // bXbX ∉ a*b*a*a
+    VERIFY(mem_unsat({{"bXbX", "a*b*a*a"}}));
+
+    // XdX ∈ (a|b)*da(a|c)*
+    VERIFY(mem_sat({{"XdX", "(a|b)*da(a|c)*"}}));
+
+    // XbX ∉ (ab)*
+    VERIFY(mem_unsat({{"XbX", "(ab)*"}}));
+
+    // XabX ∉ (ab)* && XbabX ∉ a(ba)*
+    VERIFY(mem_unsat({{"XabX","(ab)*"}, {"XbabX","a(ba)*"}}));
+
+    // XX ∉ (aba)*a
+    VERIFY(mem_unsat({{"XX", "(aba)*a"}}));
+
+    // XX ∈ (((ab)|(ba)))+aa
+    VERIFY(mem_sat({{"XX", "((ab)|(ba))+aa"}}));
+
+    // XX ∉ (ab)*a
+    VERIFY(mem_unsat({{"XX", "(ab)*a"}}));
+
+    // XX ∉ (a(a|b))*a
+    VERIFY(mem_unsat({{"XX", "(a(a|b))*a"}}));
+
+    // XX ∉ (a(a|(aaa)))*a
+    VERIFY(mem_unsat({{"XX", "(a(a|(aaa)))*a"}}));
+
+    // XX ∈ (((ab)|(ba)))+aa  (duplicate from ZIPT)
+    VERIFY(mem_sat({{"XX", "((ab)|(ba))+aa"}}));
+
+    // XX ∉ (((ab)|(ba)))+aaaa
+    VERIFY(mem_unsat({{"XX", "((ab)|(ba))+aaaa"}}));
+
+    // XX ∈ (((ab)|(ba)))*aaaa
+    VERIFY(mem_sat({{"XX", "((ab)|(ba))*aaaa"}}));
+
+    // X ∈ a+ && X ∈ b+  → UNSAT
+    VERIFY(mem_unsat({{"X","a+"}, {"X","b+"}}));
+
+    // X ∈ (a|b) && XX ∈ (a|b)  → UNSAT
+    VERIFY(mem_unsat({{"X","a|b"}, {"XX","a|b"}}));
+
+    // X ∈ (ab)+ && XX ∈ a*  → UNSAT
+    VERIFY(mem_unsat({{"X","(ab)+"}, {"XX","a*"}}));
+
+    // X ∈ a* && Y ∈ b* && XY ∈ (ab)+  → SAT
+    VERIFY(mem_sat({{"X","a*"}, {"Y","b*"}, {"XY","(ab)+"}}));
+
+    // X ∈ a* && X ∈ ~(a*)  → UNSAT
+    VERIFY(mem_unsat({{"X","a*"}, {"X","~(a*)"}}));
+
+    // X ∈ (ab)* && X ∈ (ab)+  → SAT
+    VERIFY(mem_sat({{"X","(ab)*"}, {"X","(ab)+"}}));
+
+    // X ∈ ~(a|b) && X ∈ (c|d)  → SAT
+    VERIFY(mem_sat({{"X","~(a|b)"}, {"X","c|d"}}));
+
+    // X ∈ (a|b)* && XX ∈ (ab)+  → SAT
+    VERIFY(mem_sat({{"X","(a|b)*"}, {"XX","(ab)+"}}));
+
+    // X ∈ a+ && Y ∈ b* && XYYX ∈ (ab)*(ba)*  → SAT
+    VERIFY(mem_sat({{"X","a+"}, {"Y","b*"}, {"XYYX","(ab)*(ba)*"}}));
+
+    // X ∈ (ab)+ && XXX ∈ (ab)+  → SAT
+    VERIFY(mem_sat({{"X","(ab)+"}, {"XXX","(ab)+"}}));
+
+    // X ∈ (a|b) && X ∈ ~(a|b)  → UNSAT
+    VERIFY(mem_unsat({{"X","a|b"}, {"X","~(a|b)"}}));
+
+    // X ∈ a+ && Y ∈ b+ && XY ∈ (ab)+  → SAT
+    VERIFY(mem_sat({{"X","a+"}, {"Y","b+"}, {"XY","(ab)+"}}));
+
+    // XbX ∈ a*b*  (note: same snode X shared)
+    VERIFY(mem_sat({{"XbX", "a*b*"}}));
+
+    // X ∈ a+ && XbX ∈ b*  → UNSAT
+    VERIFY(mem_unsat({{"X","a+"}, {"XbX","b*"}}));
+
+    // aXb ∈ a(a|b)*b
+    VERIFY(mem_sat({{"aXb", "a(a|b)*b"}}));
+
+    // X ∈ a+ && Y ∈ b+ && XYX ∈ (ab)*(ba)*  → SAT
+    VERIFY(mem_sat({{"X","a+"}, {"Y","b+"}, {"XYX","(ab)*(ba)*"}}));
+
+    // XX ∈ (ab|ba)+ && X ∈ (a|b)+  → SAT
+    VERIFY(mem_sat({{"XX","(ab|ba)+"}, {"X","(a|b)+"}}));
+
+    // X ∈ a* && X ∈ a+  → SAT
+    VERIFY(mem_sat({{"X","a*"}, {"X","a+"}}));
+
+    // X ∈ "" && XbX ∈ a*baa*  → UNSAT
+    VERIFY(mem_unsat({{"X",""}, {"XbX","a*baa*"}}));
+
+    // XXXX ∈ aaaaa*
+    VERIFY(mem_sat({{"XXXX", "aaaaa*"}}));
+
+    // XXXX ∉ aaa(aa)*
+    VERIFY(mem_unsat({{"XXXX", "aaa(aa)*"}}));
+
+    // XXXX ∉ ab
+    VERIFY(mem_unsat({{"XXXX", "ab"}}));
+
+    // XXXX ∉ abab
+    VERIFY(mem_unsat({{"XXXX", "abab"}}));
+
+    // XXXX ∈ a(ba)*b
+    VERIFY(mem_sat({{"XXXX", "a(ba)*b"}}));
+
+    // XXXX ∉ a(ab)*b
+    VERIFY(mem_unsat({{"XXXX", "a(ab)*b"}}));
+
+    // XYYX ∉ ab
+    VERIFY(mem_unsat({{"XYYX", "ab"}}));
+
+    // XYYX ∉ a(ab)*b
+    VERIFY(mem_unsat({{"XYYX", "a(ab)*b"}}));
+
+    // XYYX ∉ a+b+
+    VERIFY(mem_unsat({{"XYYX", "a+b+"}}));
+
+    // XaX ∈ a(a|b)*a
+    VERIFY(mem_sat({{"XaX", "a(a|b)*a"}}));
+
+    // XbY ∈ a+b* && X ∈ a* && Y ∈ b+
+    VERIFY(mem_sat({{"XbY","a+b*"}, {"X","a*"}, {"Y","b+"}}));
+
+    // X ∈ a+ && Y ∈ b+ && XbY ∉ (ab)+
+    VERIFY(mem_unsat({{"X","a+"}, {"Y","b+"}, {"XbY","(ab)+"}}));
+
+    // X ∈ ((()|a)b)* && Y ∈ (a(()|b))* && XbY ∉ (ab)*
+    VERIFY(mem_unsat({{"X","((()|a)b)*"}, {"Y","(a(()|b))*"}, {"XbY","(ab)*"}}));
+
+    // X ∈ (a(()|b))* && Y ∈ (ab)* && XbY ∈ (ab)*
+    VERIFY(mem_sat({{"X","(a(()|b))*"}, {"Y","(ab)*"}, {"XbY","(ab)*"}}));
+
+    // X ∈ (ab)* && Y ∈ ((()|a)b)* && XbY ∉ (ab)*
+    VERIFY(mem_unsat({{"X","(ab)*"}, {"Y","((()|a)b)*"}, {"XbY","(ab)*"}}));
+
+    // X ∈ (ab)* && Y ∈ (ab)* && XbY ∉ (ab)*
+    VERIFY(mem_unsat({{"X","(ab)*"}, {"Y","(ab)*"}, {"XbY","(ab)*"}}));
+
+    // X ∈ a+ && Y ∈ b+ && Z ∈ c+ && XYZ ∈ (abc)+  → SAT
+    VERIFY(mem_sat({{"X","a+"}, {"Y","b+"}, {"Z","c+"}, {"XYZ","(abc)+"}}));
+
+    // XaYbZ ∈ a*b*c* && X ∈ a* && Y ∈ b* && Z ∈ c*  → SAT
+    VERIFY(mem_sat({{"XaYbZ","a*b*c*"}, {"X","a*"}, {"Y","b*"}, {"Z","c*"}}));
+
+    // aXbYc ∈ a(a|b|c)*c
+    VERIFY(mem_sat({{"aXbYc", "a(a|b|c)*c"}}));
+
+    // X ∈ (a|b)* && Y ∈ (b|c)* && Z ∈ (c|a)* && XYZ ∈ (abc)+  → SAT
+    VERIFY(mem_sat({{"X","(a|b)*"}, {"Y","(b|c)*"}, {"Z","(c|a)*"}, {"XYZ","(abc)+"}}));
+
+    std::cout << "  ok\n";
+}
+
+// -----------------------------------------------------------------------
+// Parikh image tests  (ZIPT: CheckParikh)
+// These must be UNSAT via Parikh/letter-count arguments alone.
+// -----------------------------------------------------------------------
+static void test_zipt_parikh() {
+    std::cout << "test_zipt_parikh\n";
+
+    VERIFY(eq_unsat("abcX",      "Xbac"));
+    VERIFY(eq_unsat("XabcY",     "YbacX"));
+    VERIFY(eq_unsat("XXabcYY",   "YYbacXX"));
+    VERIFY(eq_unsat("XXacdYYb",  "YYabcdXX"));
+    VERIFY(eq_unsat("YaXaaabbbbYX", "XYababababXY"));
+
+    std::cout << "  ok\n";
+}
+
+void tst_nseq_zipt() {
+    test_zipt_str_equations();
+    test_zipt_regex_ground();
+    test_zipt_str_membership();
+    test_zipt_parikh();
+    std::cout << "nseq_zipt: all tests passed\n";
+}