. ▁Jo ined ▁points ▁represent ▁an ▁" or " ▁condition , ▁also ▁known ▁as ▁a ▁logical ▁dis j unction . ▁ ▁A ▁sp ider ▁diagram ▁is ▁a ▁boolean ▁expression ▁involving ▁unit ary ▁sp ider ▁diag rams ▁and ▁the ▁logical ▁symbols ▁. ▁For ▁example , ▁it ▁may ▁consist ▁of ▁the ▁conj unction ▁of ▁two ▁sp ider ▁diag rams , ▁the ▁dis j unction ▁of ▁two ▁sp ider ▁diag rams , ▁or ▁the ▁neg ation ▁of ▁a ▁sp ider ▁diagram . ▁ ▁Example ▁▁ ▁In ▁the ▁image ▁shown , ▁the ▁following ▁conj unction s ▁▁▁▁▁▁▁▁▁ ▁In ▁the ▁universe ▁of ▁disc ourse ▁defined ▁by ▁this ▁E uler ▁diagram , ▁in ▁addition ▁to ▁the ▁conj unction s ▁specified ▁above , ▁all ▁possible ▁sets ▁from ▁A ▁through ▁B ▁and ▁D ▁through ▁G ▁are ▁available ▁separately . ▁The ▁set ▁C ▁is ▁only ▁available ▁as ▁a ▁subset ▁of ▁B . ▁O ften , ▁in ▁complicated ▁diag rams , ▁singleton ▁sets ▁and / or ▁conj unction s ▁may ▁be ▁obsc ured ▁by ▁other ▁set ▁combinations . ▁ ▁The ▁two ▁sp iders ▁in ▁the ▁example ▁correspond ▁to ▁the ▁following ▁logical ▁expressions : ▁ ▁Red ▁sp ider : ▁ ▁Blue ▁sp ider : ▁ ▁References ▁ ▁How se , ▁J . ▁and ▁St ap leton , ▁G . ▁and ▁Taylor , ▁H . ▁Spider ▁Di agr ams ▁London ▁Mathemat ical ▁Society ▁Journal ▁of ▁Comput ation ▁and ▁Mathemat ics , ▁( 2 0 0 5 ) ▁v . ▁ 8 , ▁pp .   1 4 5 – 1 9 4 . ▁ ▁Access