Editing SKI combinator calculus (section)

== Notation ==
Although the most formal representation of the objects in this system requires binary trees, for simpler typesetting they are often represented as parenthesized expressions, as a shorthand for the tree they represent. Any subtrees may be parenthesized, but often only the right-side subtrees are parenthesized, with left associativity implied for any unparenthesized applications. For example, '''ISK''' means (('''IS''')'''K'''). Using this notation, a tree whose left subtree is the tree '''KS''' and whose right subtree is the tree '''SK''' can be written as '''KS'''('''SK'''). If more explicitness is desired, the implied parentheses can be included as well: (('''KS''')('''SK''')).