Unicode一覧 2000-2FFF
http://ja.wikipedia.org/wiki/Unicode%E4%B8%80%E8%A6%A7_2000-2FFF

font : DejaVu Serif

Two head right arrow  (U+21a0)↠
LogicalImply (U+22a8)⊧
LogicalImply (U+22a8)⊨


BOWTIE		(U+22c8)⋈
NOT SIGN	(U+00ac)¬

NEITHER A SUBSET OF NOR EQUAL TO (U+2288)⊈