[Toss-devel] Representing rules

[Lukasz S. <luk...@gm...>]

I've decided that "the signature R is extended" to mean, that in the
representation of a rule there's a partial mapping from RHS elements
to LHS elements separate from the L and R structures. It is (can be)
extracted from an "R0" structure by an auxiliary function (also given
the L). So when parsing a rule from a file, the mapping is generated
(and the RHS structure cleaned) automatically.