```ts
export function strandedTickerPairs(legs: unknown[][]): string[] {
  if (!Array.isArray(legs) || legs.length === 0) {
    throw new Error("No legs are published.");
  }

  const tickerGraph: Record<string, Set<string>> = {};

  for (const leg of legs) {
    if (!Array.isArray(leg) || leg.length !== 2) {
      throw new Error("A leg is not exactly two elements.");
    }

    const [sellTicker, buyTicker] = leg;

    if (
      typeof sellTicker !== "string" ||
      typeof buyTicker !== "string" ||
      sellTicker === "" ||
      buyTicker === ""
    ) {
      throw new Error("A ticker is not a non-empty string.");
    }

    if (sellTicker === buyTicker) {
      throw new Error("A leg sells and buys the same ticker.");
    }

    if (!tickerGraph[sellTicker]) {
      tickerGraph[sellTicker] = new Set();
    }

    if (tickerGraph[sellTicker].has(buyTicker)) {
      throw new Error("The identical leg is published twice.");
    }

    tickerGraph[sellTicker].add(buyTicker);
  }

  const tickers = Object.keys(tickerGraph);

  const canReach: Record<string, Set<string>> = {};

  const dfs = (ticker: string, visited: Set<string>) => {
    if (!canReach[ticker]) {
      canReach[ticker] = new Set();
    }
    for (const next of tickerGraph[ticker] || []) {
      if (!visited.has(next)) {
        visited.add(next);
        canReach[ticker].add(next);
        dfs(next, visited);
      }
    }
  };

  for (const ticker of tickers) {
    dfs(ticker, new Set([ticker]));
  }

  const strandedPairs: string[] = [];

  for (const fromTicker of tickers) {
    for (const toTicker of tickers) {
      if (fromTicker < toTicker && !canReach[fromTicker].has(toTicker)) {
        strandedPairs.push(`${fromTicker}>${toTicker}`);
      }
    }
  }

  return strandedPairs.sort((a, b) => a.localeCompare(b));
}
```