I,J : item
K,L : local environment
M,N : reserved: future use
-O,P,Q :
-R : generic predicate (relation)
+O :
+P : relocation environment
+Q : elimination predicate
+R : generic predicate/relation
S : RTM stack
T,U,V,W: term
X,Y,Z : reserved: transient objet denoted by a capital letter
-a :
+a : applicability condition (true = restricted, false = general)
b : local dropping kind parameter (true = restricted, false = general)
c : rt-reduction count parameter
d : term degree
2: binary
A: application to vector
+E: empty list
F: boolean false
T: boolean true