In mathematics, a Fredholm operator is an operator that arises in the Fredholm theory of integral equations. It is named in honour of Erik Ivar Fredholm. A Fredholm operator is a bounded linear operator between two Banach spaces whose kernel and cokernel are finite-dimensional and whose range is closed. (The last condition is actually redundant.[1]) Equivalently, an operator T : X Y is Fredholm if it is invertible modulo compact operators. The set of Fredholm operators from X to Y is open in the Banach space L(X, Y) of bounded linear operators, equipped with the operator norm. More precisely, when T0 is Fredholm from X to Y, there exists 0 such that every T in L(X, Y) with T T0