13G Filing: Senator Investment Group and D. R. Horton Inc (DHI)

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Exhibit 1

JOINT FILING AGREEMENT
PURSUANT TO RULE 13d-1(k)

The undersigned
acknowledge and agree that the foregoing statement on Schedule 13G is filed on behalf of each of the undersigned and that all subsequent
amendments to this statement on Schedule 13G shall be filed on behalf of each of the undersigned without the necessity of filing
additional joint acquisition statements. The undersigned acknowledge that each shall be responsible for the timely filing of such
amendments, and for the completeness and accuracy of the information concerning him or it contained therein, but shall not be responsible
for the completeness and accuracy of the information concerning the others, except to the extent that he or it knows or has reason
to believe that such information is inaccurate.

DATE: as of September 25, 2017

SENATOR INVESTMENT GROUP LP
/s/ Evan Gartenlaub
Name: Evan Gartenlaub
Title: General Counsel
/s/ Evan Gartenlaub as Attorney-in-Fact*
ALEXANDER KLABIN
/s/ Evan Gartenlaub as Attorney-in-Fact*
DOUGLAS SILVERMAN

* Pursuant to a Power of Attorney attached to the Schedule 13G filed
by the Reporting Persons on April 24, 2013.

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