Local Constraints in the Syntax and Semantics of Programming Languages. - Aravind K. Joshi; Leon S. Levy; Kang Yueh (POPL, 1978)

On labelled graph grammars. - Leon S. Levy; Kang Yueh (Computing, 1978)

Local Constraints in Programming Languages Part I: Syntax. - Aravind K. Joshi; Leon S. Levy; Kang Yueh (Theor. Comput. Sci., 1980)