New in version 2.0.
True when expr is a sequence and all elements in expr are equal:
abjad> from abjad.tools import sequencetools
abjad> sequencetools.all_are_equal([99, 99, 99, 99, 99, 99])
True
True when expr is an empty sequence:
abjad> sequencetools.all_are_equal([])
True
False otherwise:
abjad> sequencetools.all_are_equal(17)
False
Return boolean.