Frank learned to share Myrtle's love of wild flowers, and as a family they made uncounted trips in the spring and summer to seek them out. A summer cabin at Clipper Mills facilitated these activities. They established their home in the Berkeley hills, where Frank loved to walk. Many friends and former students will remember the hospitality of their home and their kindness and interest toward young people and colleagues.

It is known that a harmonic function may have zero boundary values on the circumference of a circle (for approach along radii, etc.) and still not vanish within the circle. ... [Wolf's] paper is a study of the restrictions on the order of growth of a harmonic function, as a function of r, which are sufficient to insure uniqueness, and, in particular, uniqueness of representation in terms of the Poisson integral. By means of conformal representation, simply connected domains with rectifiable boundaries are reduced to the circle.

There are seven chapters. In Chapter I [Wolf] gives some preliminary results and in Chapter II a theory of generalized integrals required in the sequel. In Chapter III he gives two fundamental theorems. The first gives, under certain rather complex conditions, inversion formulae for trigonometric integrals and the second asserts that under the same conditions the difference between the given trigonometric integral and the trigonometric series of a certain function will be uniformly summable to zero throughout a given interval. Chapter IV deals with trigonometric integrals summable over sets of positive measure and extends Kuttner's theorem and some similar results of Marcinkiewicz and Zygmund. In chapter V he extends some theorems of Hille, Offord and Tamarkin. In Chapter VI he gives some results on the inversion of order of integration in a trigonometric integral equivalent to the integration of trigonometric series term by term. Finally in the last chapter there are some very general inversion theorems which the author asserts will yield every known inversion theorem for trigonometric integrals.

Soon after he came to Berkeley, Frank's mathematical interests took a change in direction as he began to study the perturbation of linear operators. This is the theory of the behaviour of the spectral properties of an operator under small changes in the operator. Such perturbation results are important, for example, in quantum mechanics where physical phenomena are interpreted through linear operators on Hilbert space. Consideration of the Schrödinger equation leads to perturbation problems for partial differential operators, where the change may occur in the coefficients of the operator or in boundary conditions. Frank's most influential papers were probably those concerned with the analytical perturbation of operators on Banach spaces and his studies on the essential spectrum of certain singular elliptic differential operators.

Frank Wolf was a person of personal warmth and charm. He had a great interest in people and in cultural activities. He especially loved music and was accomplished on the piano and violin. For many years he served as a member of the Committee on Arts and Lectures which brought performing artists to the campus. ... Always among his strongest interests was the well-being of Czechoslovakia. He had found many Czech immigrants in Minnesota, and he was a strong supporter of the Czech community in the Bay Area. During the founding of the United Nations in San Francisco in 1945, a dispute arose in the Czechoslovak delegation, and Frank was chosen on one occasion to address the gathering on behalf of his country.