src/main/java/com/basistech/tclre/Compiler.java
private int numst(Subre t, int start) {
        int i;

        assert t != null;

        i = start;
        t.retry = (short)i++;

        if (t.left != null) {
            i = numst(t.left, i);
        }
        if (t.right != null) {
            i = numst(t.right, i);
        }
        return i;
    }
private int numst(Subre t, int start) {
        int i;

        assert t != null;

        i = start;
        t.retry = (short)i++;

        if (t.left != null) {
            i = numst(t.left, i);
        }
        if (t.right != null) {
            i = numst(t.right, i);
        }
        return i;
    }
numst - number tree nodes (assigning retry indexes)

@return next number