A contraction of "Henderson Escher", it's an implementation of Peter Henderson's functional language for the description of M. C. Escher's Square Limit as described in
Henderson, Peter. Functional Geometry. Proceedings of 1982 ACM Sym- posium on Lisp and Functional Programming, 179-187, ACM, (1982)
and
Henderson, Peter (2002) Functional Geometry Higher-Order and Symbolic Computation, 15, (4), pp. 349-365.