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n |
A type
definition may be a restriction of
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another type's
definition if it reduces
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permissions,
sometimes to the point of
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inducing
obligations:
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\d[01]\d-\d{3}-\d{4} (a
restriction
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(\d )?(\d{3}-)?\d{3}-\d{4} of US p#)
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n |
The
membership of this type, which includes
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ä |
207-422-6240 but not 1 337-6818
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n |
is a (proper)
subset of the membership of the
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original type,
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n |
because by
construction every member of the
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new type is a
member of the original.
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