Substitutions

Substitutions are expressions of the form [... => ...] replacing an entity by another.

Variables

Variables can be replaced by any other ray:

show-exec (+f(X))[X=>Y].
show-exec (+f(X))[X=>+a(X)].

Function symbols

Function symbols can be replaced by other function symbols:

show-exec (+f(X))[+f=>+g].
show-exec (+f(X))[+f=>f].

We can also omit the left or right part of => to add or remove a head symbol:

show-exec (+f(X); f(X))[=>+a].
show-exec (+f(X); f(X))[=>a].
show-exec (+f(X); f(X))[+f=>].

Constellation identifiers

show-exec (#1 #2)[#1=>+f(X) X][#2=>-f(a)].