Definition
Lambda Variable
The set of variable symbols is defined as :
Bound
Bound Lambda Variable
A variable is called bound if it is introduced by a
within the expression and falls within the scope of that . Examples:
: both instances of are bound by the .
Free
Free Lambda Variable
A variable is called free if it appears in the expression but it is not bound by any enclosing
within that specific expression. Examples:
: the variable is free because there’s no binding it.