You have been asked to select at least 3 out of 7 possible sites for oil exploration. Designate each site as S1, S2, S3,

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You have been asked to select at least 3 out of 7 possible sites
for oil exploration. Designate each site as S1, S2, S3, S4, S5, S6,
and S7. The restrictions are: Restriction 1. Evaluating sites S1
and S3 will prevent you from exploring site S7. Restriction 2.
Evaluating sites S2 and S4 will prevent you from assessing site S5.
Restriction 3. Of all the sites, at least 3 should be assessed.
Assuming that Si is a binary variable, write the constraint(s) for
the second restriction.
S1 + S3 + S7 ≤ 2.
S2 + S4 + S5 ≤ 2
S2 + S4 ≤ 2, S4 + S5 ≤ 1
S4 + S5 ≤ 1