if (isEmpty(s)) {
            return false;
        }

        final int size = s.length();
        for (int i = 0; i < size; i++) {
            final char chr = s.charAt(i);
            if (chr < '0' || '9' < chr) {
                return false;
            }
        }

        return true;
    }

    /**
     * 引数の文字列を返します。引数の文字列が<code>null</code>だったら空文字を返します。
     * <p>

					i, vals, names[i], i)
			} else {
				// Normal SSA value
				fmt.Fprintf(f, "\t\tnode%d [label=<%s <font point-size=\"6\">[%d]</font>>]\n", i, names[i], i)
			}
			chl, chr := po.children(i)
			for _, ch := range []posetEdge{chl, chr} {
				if ch != 0 {
					if ch.Strict() {
						fmt.Fprintf(f, "\t\tnode%d -> node%d [label=\" <\" color=\"red\"]\n", i, ch.Target())
					} else {

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