X,Y,Z : reserved: transient objet denoted by a capital letter
a,b : binder polarity
-c : reserved: future use (\lambda\delta 3)
-d : relocation depth
-e : relocation height
+c : relocation
+d : term degree
+e : reserved: future use (\lambda\delta 3)
f :
g : sort degree parameter
h : sort hierarchy parameter
i,j : local reference position index (de Bruijn's)
k : sort index
-l : term degree
-m,n : reserved: future use
+l : relocation depth
+m : relocation height
+n : type iterations
o :
p,q : global reference position
r : reduction kind parameter (true = ordinary, false = extended)