The Church numeral for a nonnegative integer 
is the lambda term 
, which represents 
by repeated function application.
Thus zero returns 
,
while the successor adds one further application of
. Addition and multiplication are expressible
directly as operations on Church numerals.
Church Numeral
See also
Integer, Lambda Calculus, Recursive FunctionExplore with Wolfram|Alpha
References
Barendregt, H. P. The Lambda Calculus: Its Syntax and Semantics. Amsterdam, Netherlands: North-Holland, 1984.Cite this as:
Weisstein, Eric W. "Church Numeral." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/ChurchNumeral.html