Apart from new examples and exercises, some simplifications of proofs,
minor improvements, and correction of typographical errors, the
principal change from the first edition is the addition of section 9.5,
dealing with the central limit theorem for martingales and more general
stochastic arrays. vii Preface to the First Edition Probability theory
is a branch of mathematics dealing with chance phenomena and has clearly
discernible links with the real world. The origins of the sub- ject,
generally attributed to investigations by the renowned French mathe-
matician Fermat of problems posed by a gambling contemporary to Pascal,
have been pushed back a century earlier to the Italian mathematicians
Cardano and Tartaglia about 1570 (Ore, 1953). Results as significant as
the Bernoulli weak law of large numbers appeared as early as 1713,
although its counterpart, the Borel strong law oflarge numbers, did not
emerge until 1909. Central limit theorems and conditional probabilities
were already being investigated in the eighteenth century, but the first
serious attempts to grapple with the logical foundations of probability
seem to be Keynes (1921), von Mises (1928; 1931), and Kolmogorov (1933).