$\forall$${\it es}$:ES, $P$:(E$\rightarrow\mathbb{P}$), $R$:(E$\rightarrow$E$\rightarrow\mathbb{P}$). single{-}thread{-}generator\{i:l\}(${\it es}$;$P$;$R$) $\in$ $\mathbb{P}$