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A function with no free variables. A term iseither a constant, a variable or of the form A B denoting theapplication of term A (a function of one argument) to termB. Juxtaposition associates to the left in the absence ofparentheses. All combinators can be defined from two basiccombinators - S and K. These two and a third, I, are definedthus:S f g x= f x (g x)K x y= xI x= x= S K K xThere is a simple translation between combinatory logic andlambda-calculus. The size of equivalent expressions in thetwo languages are of the same order.Other combinators were added by David Turner in 1979 when heused combinators to implement SASL:B f g x = f (g x)C f g x = f x gS' c f g x = c (f x) (g x)B* c f g x = c (f (g x))C' c f g x = c (f x) gSee fixed point combinator, curried function,supercombinators.