Lambda the Ultimate

I did a search and could not find any references on LtU about "LMNtal":
http://www.ueda.info.waseda.ac.jp/~ueda/pub/chrworkshop-ueda.pdf

Abstract. LMNtal (pronounced “elemental”) is a simple language model
based on hierarchical graph rewriting that uses logical variables to represent
connectivity and membranes to represent hierarchy. LMNtal is an
outcome of the attempt to unify constraint-based concurrency and Constraint
Handling Rules (CHR), the two notable extensions to concurrent
logic programming. LMNtal is intended to be a substrate language of
various computational models, especially those addressing concurrency,
mobility and multiset rewriting. Another important goal of LMNtal has
been to put hierarchical graph rewriting into practice and demonstrate
its versatility by designing and implementing a full-fledged, monolithic
programming language. In this paper, we demonstrate the practical aspects
of LMNtal using a number of examples taken from diverse areas
of computer science. Also, we discuss the relationship between LMNtal
and CHR, which exhibit both commonalities and differences in various
respects.

It supports hierarchical structures using "membranes" and graph structures using "links", and concurrency via concurrent constraint programming and (some part of) constraint handling rules.