When the GST was originally enacted, most state laws included the common law Rule against Perpetuities (RAP) or some similar rule.

FORBES: Obama Estate Tax Budget Proposals

It's probably hard to plan a year off if your wits have been dulled by the Uniform Commercial Code and the Rule Against Perpetuities.

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To enable these trusts, most of the states allowing them had to get rid of an old common-law principle called the "rule against perpetuities, " which allowed trusts to exist only for about 90 years.

WSJ: Tax Report: Dynasty Trusts Under Attack