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+// Connect IV — Play against a perfect AI
+// Minimax with alpha-beta pruning + center-first move ordering
+// You are X (player I), AI is O (player II)
+// Enter column as Roman numeral I-VII
+
+// Returns the bottommost empty row in col, or NVLLVS if full
+DEFINI find_slot(b, col) VT {
+  DESIGNA ans VT NVLLVS
+  DONICVM r VT I VSQVE VII FACE {
+    SI b[(r - I) * VII + col] EST NVLLVS TVNC {
+      DESIGNA ans VT r
+    }
+  }
+  REDI(ans)
+}
+
+// Returns VERITAS if player has four in a row
+DEFINI est_victor(b, player) VT {
+  DONICVM r VT I VSQVE VII FACE {
+    DONICVM c VT I VSQVE V FACE {
+      DESIGNA idx VT (r - I) * VII + c
+      SI b[idx] EST player ET b[idx + I] EST player ET b[idx + II] EST player ET b[idx + III] EST player TVNC {
+        REDI(VERITAS)
+      }
+    }
+  }
+  DONICVM r VT I VSQVE IV FACE {
+    DONICVM c VT I VSQVE VIII FACE {
+      DESIGNA idx VT (r - I) * VII + c
+      SI b[idx] EST player ET b[idx + VII] EST player ET b[idx + XIV] EST player ET b[idx + XXI] EST player TVNC {
+        REDI(VERITAS)
+      }
+    }
+  }
+  DONICVM r VT I VSQVE IV FACE {
+    DONICVM c VT I VSQVE V FACE {
+      DESIGNA idx VT (r - I) * VII + c
+      SI b[idx] EST player ET b[idx + VIII] EST player ET b[idx + XVI] EST player ET b[idx + XXIV] EST player TVNC {
+        REDI(VERITAS)
+      }
+    }
+  }
+  DONICVM r VT I VSQVE IV FACE {
+    DONICVM c VT IV VSQVE VIII FACE {
+      DESIGNA idx VT (r - I) * VII + c
+      SI b[idx] EST player ET b[idx + VI] EST player ET b[idx + XII] EST player ET b[idx + XVIII] EST player TVNC {
+        REDI(VERITAS)
+      }
+    }
+  }
+  REDI(FALSITAS)
+}
+
+DEFINI print_board(b) VT {
+  DICE("+---+---+---+---+---+---+---+")
+  DONICVM r VT I VSQVE VII FACE {
+    DESIGNA line VT "| "
+    DONICVM c VT I VSQVE VIII FACE {
+      DESIGNA cell VT b[(r - I) * VII + c]
+      SI cell EST I TVNC {
+        DESIGNA line VT line & "X | "
+      } ALVID SI cell EST II TVNC {
+        DESIGNA line VT line & "O | "
+      } ALVID {
+        DESIGNA line VT line & ". | "
+      }
+    }
+    DICE(line)
+  }
+  DICE("+---+---+---+---+---+---+---+")
+  DICE("  I   II III IV   V   VI VII")
+  REDI(NVLLVS)
+}
+
+// Score a 4-cell window: positive favours AI (II), negative favours player (I).
+// Only scores windows that are not mixed (one side can still win them).
+DEFINI score_fenestram(a, b, c, d) VT {
+  DESIGNA ai VT NVLLVS
+  DESIGNA pl VT NVLLVS
+  SI a EST II TVNC { DESIGNA ai VT ai + I }
+  SI b EST II TVNC { DESIGNA ai VT ai + I }
+  SI c EST II TVNC { DESIGNA ai VT ai + I }
+  SI d EST II TVNC { DESIGNA ai VT ai + I }
+  SI a EST I TVNC { DESIGNA pl VT pl + I }
+  SI b EST I TVNC { DESIGNA pl VT pl + I }
+  SI c EST I TVNC { DESIGNA pl VT pl + I }
+  SI d EST I TVNC { DESIGNA pl VT pl + I }
+  SI pl EST NVLLVS TVNC {
+    SI ai EST III TVNC { REDI(V) }
+    SI ai EST II TVNC { REDI(II) }
+  }
+  SI ai EST NVLLVS TVNC {
+    SI pl EST III TVNC { REDI(NVLLVS - V) }
+    SI pl EST II TVNC { REDI(NVLLVS - II) }
+  }
+  REDI(NVLLVS)
+}
+
+// Static board evaluation: scan all 69 windows of 4 cells.
+// Returns a score in roughly [-350, 350]; positive = AI advantage.
+DEFINI aestima(b) VT {
+  DESIGNA score VT NVLLVS
+  // Center column preference: each AI piece in column IV is worth +1
+  DONICVM r VT I VSQVE VII FACE {
+    SI b[(r - I) * VII + IV] EST II TVNC {
+      DESIGNA score VT score + I
+    }
+  }
+  // Horizontal windows (6 rows x 4 starting columns = 24)
+  DONICVM r VT I VSQVE VII FACE {
+    DONICVM c VT I VSQVE V FACE {
+      DESIGNA idx VT (r - I) * VII + c
+      DESIGNA score VT score + INVOCA score_fenestram(b[idx], b[idx + I], b[idx + II], b[idx + III])
+    }
+  }
+  // Vertical windows (3 starting rows x 7 columns = 21)
+  DONICVM r VT I VSQVE IV FACE {
+    DONICVM c VT I VSQVE VIII FACE {
+      DESIGNA idx VT (r - I) * VII + c
+      DESIGNA score VT score + INVOCA score_fenestram(b[idx], b[idx + VII], b[idx + XIV], b[idx + XXI])
+    }
+  }
+  // Diagonal up-right windows (3 starting rows x 4 starting columns = 12)
+  DONICVM r VT I VSQVE IV FACE {
+    DONICVM c VT I VSQVE V FACE {
+      DESIGNA idx VT (r - I) * VII + c
+      DESIGNA score VT score + INVOCA score_fenestram(b[idx], b[idx + VIII], b[idx + XVI], b[idx + XXIV])
+    }
+  }
+  // Diagonal up-left windows (3 starting rows x 4 starting columns = 12)
+  DONICVM r VT I VSQVE IV FACE {
+    DONICVM c VT IV VSQVE VIII FACE {
+      DESIGNA idx VT (r - I) * VII + c
+      DESIGNA score VT score + INVOCA score_fenestram(b[idx], b[idx + VI], b[idx + XII], b[idx + XVIII])
+    }
+  }
+  REDI(score)
+}
+
+// Minimax with alpha-beta pruning and depth-limited aestima evaluation.
+// depth = remaining search plies (counts down from a fixed budget).
+// Wins score ±(M + depth) so the search always prefers quicker wins and
+// delays losses; aestima values stay well within ±M so wins dominate.
+DEFINI minimax(b, depth, alpha, beta, maxi) VT {
+  SI maxi TVNC {
+    SI INVOCA est_victor(b, I) TVNC {
+      REDI(NVLLVS - M - depth)
+    }
+  } ALVID {
+    SI INVOCA est_victor(b, II) TVNC {
+      REDI(M + depth)
+    }
+  }
+  SI depth EST I TVNC {
+    REDI(INVOCA aestima(b))
+  }
+  DESIGNA col_order VT [IV, III, V, II, VI, I, VII]
+  SI maxi TVNC {
+    DESIGNA best VT NVLLVS - M - VII
+    PER c IN col_order FACE {
+      DESIGNA linea VT INVOCA find_slot(b, c)
+      SI NON (linea EST NVLLVS) TVNC {
+        DESIGNA b[(linea - I) * VII + c] VT II
+        DESIGNA score VT INVOCA minimax(b, depth - I, alpha, beta, FALSITAS)
+        DESIGNA b[(linea - I) * VII + c] VT NVLLVS
+        SI score PLVS best TVNC {
+          DESIGNA best VT score
+        }
+        SI best PLVS alpha TVNC {
+          DESIGNA alpha VT best
+        }
+        SI beta MINVS alpha AVT beta EST alpha TVNC {
+          ERVMPE
+        }
+      }
+    }
+    REDI(best)
+  } ALVID {
+    DESIGNA best VT M + VII
+    PER c IN col_order FACE {
+      DESIGNA linea VT INVOCA find_slot(b, c)
+      SI NON (linea EST NVLLVS) TVNC {
+        DESIGNA b[(linea - I) * VII + c] VT I
+        DESIGNA score VT INVOCA minimax(b, depth - I, alpha, beta, VERITAS)
+        DESIGNA b[(linea - I) * VII + c] VT NVLLVS
+        SI score MINVS best TVNC {
+          DESIGNA best VT score
+        }
+        SI best MINVS beta TVNC {
+          DESIGNA beta VT best
+        }
+        SI beta MINVS alpha AVT beta EST alpha TVNC {
+          ERVMPE
+        }
+      }
+    }
+    REDI(best)
+  }
+}
+
+// Pick the best column for the AI (depth VI = 5 plies of lookahead)
+DEFINI ai_move(b) VT {
+  DESIGNA col_order VT [IV, III, V, II, VI, I, VII]
+  DESIGNA best_score VT NVLLVS - M - VII
+  DESIGNA best_col VT IV
+  PER c IN col_order FACE {
+    DESIGNA linea VT INVOCA find_slot(b, c)
+    SI NON (linea EST NVLLVS) TVNC {
+      DESIGNA b[(linea - I) * VII + c] VT II
+      DESIGNA score VT INVOCA minimax(b, VI, NVLLVS - M - VII, M + VII, FALSITAS)
+      DESIGNA b[(linea - I) * VII + c] VT NVLLVS
+      SI score PLVS best_score TVNC {
+        DESIGNA best_score VT score
+        DESIGNA best_col VT c
+      }
+    }
+  }
+  REDI(best_col)
+}
+
+// --- Board setup ---
+DESIGNA board VT [I VSQVE XLIII]
+DONICVM i VT I VSQVE XLIII FACE {
+  DESIGNA board[i] VT NVLLVS
+}
+
+DESIGNA moves VT NVLLVS
+DESIGNA game_over VT FALSITAS
+
+DICE("=== CONNECT IV ===")
+DICE("You are X. AI is O.")
+DICE("Enter column as Roman numeral (I-VII).")
+DICE("")
+
+DVM game_over FACE {
+  EVERRO()
+  INVOCA print_board(board)
+
+  DICE("Your move:")
+  DESIGNA col VT AVDI_NVMERVS()
+  SI col PLVS VII TVNC {
+    DICE("Invalid column! Enter I through VII.")
+    CONTINVA
+  }
+  DESIGNA linea VT INVOCA find_slot(board, col)
+  SI linea EST NVLLVS TVNC {
+    DICE("Column full! Try another.")
+    CONTINVA
+  }
+  DESIGNA board[(linea - I) * VII + col] VT I
+  DESIGNA moves VT moves + I
+  SI INVOCA est_victor(board, I) TVNC {
+    INVOCA print_board(board)
+    DICE("You win!")
+    DESIGNA game_over VT VERITAS
+    CONTINVA
+  }
+  SI moves EST XLII TVNC {
+    INVOCA print_board(board)
+    DICE("Draw!")
+    DESIGNA game_over VT VERITAS
+    CONTINVA
+  }
+
+  DICE("AI is thinking...")
+  DESIGNA col VT INVOCA ai_move(board)
+  DESIGNA linea VT INVOCA find_slot(board, col)
+  DICE("AI plays column " & col & ".")
+  DESIGNA board[(linea - I) * VII + col] VT II
+  DESIGNA moves VT moves + I
+  SI INVOCA est_victor(board, II) TVNC {
+    INVOCA print_board(board)
+    DICE("AI wins!")
+    DESIGNA game_over VT VERITAS
+    CONTINVA
+  }
+  SI moves EST XLII TVNC {
+    INVOCA print_board(board)
+    DICE("Draw!")
+    DESIGNA game_over VT VERITAS
+  }
+}