, 1 )- s parse ▁graphs , ▁and ▁the ▁independent ▁rig id ▁sets ▁form ▁the ▁edge ▁sets ▁of ▁trees , ▁( 1 , 1 )- t ight ▁graphs . ▁In ▁this ▁case ▁the ▁rig id ity ▁mat roid ▁of ▁a ▁framework ▁is ▁the ▁same ▁as ▁the ▁graph ic ▁mat roid ▁of ▁the ▁corresponding ▁graph . ▁ ▁In ▁two ▁dimensions , ▁ ▁showed ▁that ▁the ▁same ▁character ization ▁is ▁true : ▁the ▁independent ▁sets ▁form ▁the ▁edge ▁sets ▁of ▁( 2 , 3 )- s parse ▁graphs ▁and ▁the ▁independent ▁rig id ▁sets ▁form ▁the ▁edge ▁sets ▁of ▁( 2 , 3 )- t ight ▁graphs . ▁Based ▁on ▁this ▁work ▁the ▁( 2 , 3 )- t ight ▁graphs ▁( the ▁graphs ▁of ▁minim ally ▁rig id ▁generic ▁frameworks ▁in ▁two ▁dimensions ) ▁have ▁come ▁to ▁be ▁known ▁as ▁Lam an ▁graphs . ▁The ▁family ▁of ▁Lam an ▁graphs ▁on ▁a ▁fixed ▁set ▁of ▁ ▁vertices ▁forms ▁the ▁set ▁of ▁bases ▁of ▁the ▁rig id ity ▁mat roid ▁of ▁a ▁complete ▁graph , ▁and ▁more ▁generally ▁for ▁every ▁graph ▁ ▁that ▁forms ▁a ▁rig id ▁framework ▁in ▁two ▁dimensions , ▁the ▁sp anning ▁Lam an ▁sub graph s ▁of ▁ ▁are ▁the ▁bases ▁of ▁the ▁rig id ity ▁mat roid ▁of ▁. ▁ ▁However , ▁in ▁higher ▁dimensions ▁not ▁every ▁- t ight ▁graph ▁is ▁minim ally ▁rig id , ▁and ▁character izing ▁the ▁minim ally ▁rig id ▁graphs ▁( the ▁bases ▁of ▁the ▁rig id ity ▁mat roid ▁of ▁the ▁complete ▁graph