Alan Josentential form:
math: S \Longrightarrow^* \alpha \,\,and\,\, \alpha \in (V\cup U)^*left-sentential form:
math: S \Longrightarrow_{lm}^* \alpharight-sentential form:
math: S \Longrightarrow_{rm}^* \alphaL(G) element is same with sentential form which are in T*