We show that for a relation f 0 1 n and a function g : 0 1 m 0 1 m 0 1 (with m = O ( log n ) ), R 1 3 ( f g n ) = R 1 3 ( f ) log 1 disc ( M g ) − O ( log n ) where f g n represents the composition of f and g n , M g is the sign matrix for g , disc ( M g ) is the discrepancy of M g under the uniform distribution and R 1 3 ( f ) ( R 1 3 ( f g n ) ) denotes the randomized query complexity of f (randomized communication complexity of f g n ) with worst case error 3 1 .
In particular, this implies that for a relation f 0 1 n , R 1 3 ( f IP n m ) = R 1 3 ( f ) m where IP m : 0 1 m 0 1 m 0 1 is the Inner Product (modulo 2 ) function and m = O ( log ( n )) .