Dan's father, Isaac, was born in the Ukraine in 1888. Dan's grandfather Joseph emigrated to the U.S. in 1896, and brought the rest of the family over four years later.

In high school, mathematics was my favourite subject. I especially enjoyed challenging problems. But I did not know that mathematics was a profession. I am indebted to my high school English teacher who, in my senior year, called me up to his desk to ask about my career plans, and told me that his brother was a mathematician. I decided then and there that mathematics was for me.

... he did not know whether he would have enough income to pay the high Princeton rents. After a consultation, the Institute offered him free rent. He immediately proposed marriage to Evelyn, and after a honeymoon in Nantucket, they moved to the Institute.

The results in this paper were obtained by the author in his doctoral dissertation. The author wishes to acknowledge his debt to Prof Garrett Birkhoff for his very valuable advice and encouragement.

One of the problems early in the history of continuous groups was the determination of all the continuous groups of transformations in the line, plane, and n-space. Sophus Lie derived all the then-called "groups" of transformations in the line and plane. An inspection of his methods reveals that what he obtained was all the local Lie groups of transformations defined in a neighborhood of Euclidean space. It is natural to wonder whether a local group of transformations defined on a neighborhood of the line, plane, or more generally a region of n-space can be extended to a global group of transformations on a manifold of which the given region is a subset. ... In this paper it is proved that a local Lie transitive group of transformations defined in a neighborhood of Euclidean space of dimension less than five can be extended to a global Lie transitive group of transformations on some manifold; if the dimension of the neighborhood is five or greater, the extensibility is not always possible.

E Cartan has proved that a connected semi-simple Lie group is topologically the direct product of a compact subgroup and a Euclidean space. Cartan first proved this theorem in 1927 by a reduction to special cases, and not until 1929 did he free his proof from the consideration of special cases. As a result Cartan's proof is diffused among several journals. Moreover, Cartan employs in an essential way the theory of symmetric Riemannian spaces and makes use of a result whose proof seems to be lacking. ...

In this paper there will be given a more direct proof which eliminates the use of symmetric Riemannian spaces. The author wishes to acknowledge his debt to Professor C Chevalley who suggested in an oral communication Lemma 1.4 below and to whom a proof of Theorem 1, essentially the same as the one given here, was known.

Reading history, especially the history of religion. Trying to understand what is the good life and living a good life. It helps to have a loving wife, four children, and their spouses, as well as 10 grandchildren and 14 great-grandchildren, all fascinating. I enjoy singing in a chorus, and attending the high-definition Metropolitan opera performances at Yale. The University's Koerner Center for Emeritus Faculty - which has a rich program of lectures, films, and parties - keeps me in contact with colleagues from other departments.

George D Mostow made a fundamental and pioneering contribution to geometry and Lie group theory. His most celebrated accomplishment in this fields is the discovery of the completely new rigidity phenomenon in geometry, the Strong Rigidity Theorems. These theorems are some of the greatest achievements in mathematics in the second half of the 20th century. This established a deep connection between continuous and discrete groups, or equivalently, a remarkable connection between topology and geometry. Mostow's rigidity methods and techniques opened a floodgate of investigations and results in many related areas of mathematics. Mostow's emphasis on the "action at infinity" has been developed by many mathematicians in a variety of directions. It had a huge impact in geometric group theory, in the study of Kleinian groups and of low dimensional topology, in work connecting ergodic theory and Lie groups. Mostow's contribution to mathematics is not limited to strong rigidity theorems. His work on Lie groups and their discrete subgroups which was done during 1948-1965 was very influential. Mostow's work on examples of nonarithmetic lattices in two and three dimensional complex hyperbolic spaces (partially in collaboration with P Deligne) is brilliant and lead to many important developments in mathematics. In Mostow's work one finds a stunning display of a variety of mathematical disciplines. Few mathematicians can compete with the breadth, depth, and originality of his works.