${\text{LDL}}_f\mathit{\text{formula }}\phi$

$\mathit{\text{Proposition }}\psi$ $::={\text{LDL}}_f\mathit{\text{formula w/o modality}}$

$\mathit{\text{Regular path }}\rho$ $::=\psi \mid \phi \mathrm{?}\mid {\rho }_1+{\rho }_2\mid {\rho }_1;{\rho }_2\mid {\rho }^{\ast }$

$\mathit{\text{Atomic proposition }}A$ $::=\mathbf{\text{true}}\mid \mathbf{\text{false}}\mid \mathit{\text{symbol}}$