[2] Mead sold Lexis, and Illinois maintained that Mead must pay them a proportionate capital-gains tax.

[3] Illinois asserted that Mead and Lexis were integrated to the extent required for the "unitary business rule".

[4] This rule allowed states to tax a proportionate share of the value generated by an interstate corporation.

[5] In a unanimous opinion written by Associate Justice Samuel Alito, the Supreme Court held that the two businesses were not integrated enough to be considered a "unitary business" and Illinois was not allowed to tax Mead on the Lexis sale.

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