POWER OF ATTORNEY

      Know all by these presents, that the undersigned hereby constitutes and
appoints each of Chris W. Trester and Yujin Yi of Gibson, Dunn & Crutcher LLP,
with full power of substitution, the undersigned's true and lawful
attorney-in-fact to:

      1.  prepare, execute in the undersigned's name and on the undersigned's
          behalf, and submit to the U.S. Securities and Exchange Commission
          (the "SEC"), a Form ID, including amendments thereto, and any other
          documents necessary or appropriate to obtain codes and passwords
          enabling the undersigned to make electronic filings with the SEC of
          reports required by the Securities Exchange Act of 1934 or any
          rule or regulation of the SEC;

      2.  do and perform any and all acts for and on behalf of the undersigned
          which may be necessary or desirable to complete and execute such
          Form ID and file such form with the SEC and any stock exchange or
          similar authority; and

      3.  execute for and on behalf of the undersigned, in the undersigned's
          capacity as a member, manager, director and/or officer or beneficial
          owner, Forms 3, 4, and 5 in accordance with Section 16(a) of the
          Securities Exchange Act of 1934 and the rules thereunder;

      4.  do and perform any and all acts for and on behalf of the undersigned
          which may be necessary or desirable to complete and execute any such
          Form 3, 4, or 5, complete and execute any amendment or amendments
          thereto, and timely file such form with the SEC and any securities
          exchange or similar authority; and

      3.  take any other action of any type whatsoever in connection with the
          foregoing which, in the opinion of such attorney-in-fact, may be of
          benefit to, in the best interest of, or legally required by, the
          undersigned, it being understood that the documents executed by such
          attorney-in-fact on behalf of the undersigned pursuant to this Power
          of Attorney shall be in such form and shall contain such terms and
          conditions as such attorney-in-fact may approve in such attorney-in-
          fact's discretion.

      The undersigned hereby grants to such attorneys-in-fact full power and
authority to do and perform any and every act and thing whatsoever requisite,
necessary, or proper to be done in the exercise of any of the rights and powers
herein granted, as fully to all intents and purposes as the undersigned might or
could do if personally present, with full power of substitution or revocation,
hereby ratifying and confirming all that such attorney-in-fact, or such
attorney-in-fact's substitute or substitutes, shall lawfully do or cause to be
done by virtue of this power of attorney and the rights and powers herein
granted.  The undersigned acknowledges that the foregoing attorneys-in-fact, in
serving in such capacity at the request of the undersigned, are not assuming,
any of the undersigned's responsibilities to comply with the Securities Exchange
Act of 1934 or any rule or regulation of the SEC.

      This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to (a) file a Form ID, or any amendments or
changes thereto, with respect to the undersigned's holdings of and transactions
in securities issued by the undersigned, (b) the undersigned is no longer
required to file Forms 3, 4, and 5 with respect to the undersigned's holdings or
(c) revocation by the undersigned in a signed writing delivered to the foregoing
attorneys-in-fact.


      IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to
be executed as of this 23rd day of October, 2020.


                                            /s/Jonathan Violin
                                            -----------------------------------
                                            Jonathan Violin, an Individual