k,l : global reference level
m :
n : type iterations
-o : sort degree parameter
+o : sort degree parameter (origin)
p,q : binder polarity
-r : reduction kind parameter (true = ordinary, false = extended)
+r :
s : sort index
t,u :
v,w : local reference position level (de Bruijn's) (RTM)
c: conversion
d: decomposed rt-reduction
e: decomposed rt-conversion
-g: generic rt-transition
+g: counted rt-transition (generic)
+m: semi-counted rt-transition (mixed)
q: restricted reduction
r: reduction
s: substitution
u: supclosure
w: reserved for generic pointwise extension
-x: rt-reduction
+x: uncounted rt-transition (extended)
y: rt-substitution
- forth letter (if present)