Free Choice (FC) structure: if two transitions share a common input place then they have no other input places;
Extended Free Choice (EFC) structure: if two transitions have common input places they have no other input places;
Behaviourally Free Choice (BFC) structure: if two transitions have common input places, then, if a marking enables one of them it enables also the other one;
Asymmetric Choice (AC) structure: if two places have common input transitions then the set of input transitions of the one is a subset of the set of input transitions of the other;
Reduced Asymmetric Choice (RAC) Nets allow all FC structures having no more than two input places for each transition and only one type of non-FC structure;